krpc: Display stats of TLS usage

This patch adds some sysctls:
kern.rpc.unenc.tx_msgcnt
kern.rpc.unenc.tx_msgbytes
kern.rpc.unenc.rx_msgcnt
kern.rpc.unenc.rx_msgbytes
kern.rpc.tls.tx_msgcnt
kern.rpc.tls.tx_msgbytes
kern.rpc.tls.rx_msgcnt
kern.rpc.tls.rx_msgbytes
kern.rpc.tls.handshake_success
kern.rpc.tls.handshake_failed
kern.rpc.tls.alerts
which allow a NFS server sysadmin to determine how much
NFS-over-TLS is being used. A large number of failed
handshakes might also indicate an NFS confirguration
problem.

This patch moves the definition of "kern.rpc" from the
kgssapi module to the krpc module. As such, both modules
need to be rebuilt from sources. Since __FreeBSD_version
was bumped yesterday, I will not bump it again.

Suggested by: gwollman
Discussed on: freebsd-current
MFC after: 1 month

sys: Remove $FreeBSD$: two-line .h pattern

Remove /^\s*\*\n \*\s+\$FreeBSD\$$\n/

spdx: The BSD-2-Clause-FreeBSD identifier is obsolete, drop -FreeBSD

The SPDX folks have obsoleted the BSD-2-Clause-FreeBSD identifier. Catch
up to that fact and revert to their recommended match of BSD-2-Clause.

Discussed with: pfg
MFC After: 3 days
Sponsored by: Netflix

nfsd: Add VNET_SYSUNINIT() macros for vnet cleanup

Commit ed03776ca7f4 enabled the vnet front end macros.
As such, for kernels built with the VIMAGE option will malloc
data and initialize locks on a per-vnet basis, typically
via a VNET_SYSINIT().

This patch adds VNET_SYSUNINIT() macros to do the frees
of the per-vnet malloc'd data and destroys of per-vnet
locks. It also removes the mtx_lock/mtx_unlock calls
from nfsrvd_cleancache(), since they are not needed.

Discussed with: bz, jamie
MFC after: 3 months

nfsd: Enable the NFSD_VNET vnet front end macros

Several commits have added front end macros for the vnet
macros to the NFS server, krpc and kgssapi. These macros
are now null, but this patch changes them to front end
the vnet macros.

With this commit, many global variables in the code become
vnet'd, so that nfsd(8), nfsuserd(8), rpc.tlsservd(8) and
gssd(8) can run in a vnet prison, once enabled.
To run the NFS server in a vnet prison still requires a
couple of patches (in D37741 and D38371) that allow mountd(8)
to export file systems from within a vnet prison. Once
these are committed to main, a small patch to kern_jail.c
allowing "allow.nfsd" without VNET_NFSD defined will allow
the NFS server to run in a vnet prison.

One area that still needs to be settled is cleanup when a
prison is removed. Without this, everything should work
except there will be a leak of malloc'd data and mutex locks
when a vnet prison is removed.

MFC after: 3 months

krpc: Add macros so that rpc.tlsservd can run in vnet prison

Commit 7344856e3a6d added a lot of macros that will front end
vnet macros so that nfsd(8) can run in vnet prison.
This patch adds similar macros named KRPC_VNETxxx so that
the rpc.tlsservd(8) daemon can run in a vnet prison, once the
macros front end the vnet ones. For now, they are null macros.

MFC after: 3 months

nfsd: Allow multiple instances of rpc.tlsservd

During a discussion with someone working on NFS-over-TLS
for a non-FreeBSD platform, we agreed that a single server
daemon for TLS handshakes could become a bottleneck when
an NFS server first boots, if many concurrent NFS-over-TLS
connections are attempted.

This patch modifies the kernel RPC code so that it can
handle multiple rpc.tlsservd daemons. A separate commit
currently under review as D35886 for the rpc.tlsservd
daemon.

Add a new "tlscertname" NFS mount option.

When using NFS-over-TLS, an NFS client can optionally provide an X.509
certificate to the server during the TLS handshake. For some situations,
such as different NFS servers or different certificates being mapped
to different user credentials on the NFS server, there may be a need
for different mounts to provide different certificates.

This new mount option called "tlscertname" may be used to specify a
non-default certificate be provided. This alernate certificate will
be stored in /etc/rpc.tlsclntd in a file with a name based on what is
provided by this mount option.

Add TLS support to the kernel RPC.

An internet draft titled "Towards Remote Procedure Call Encryption By Default"
describes how TLS is to be used for Sun RPC, with NFS as an intended use case.
This patch adds client and server support for this to the kernel RPC,
using KERN_TLS and upcalls to daemons for the handshake, peer reset and
other non-application data record cases.

The upcalls to the daemons use three fields to uniquely identify the
TCP connection. They are the time.tv_sec, time.tv_usec of the connection
establshment, plus a 64bit sequence number. The time fields avoid problems
with re-use of the sequence number after a daemon restart.
For the server side, once a Null RPC with AUTH_TLS is received, kernel
reception on the socket is blocked and an upcall to the rpctlssd(8) daemon
is done to perform the TLS handshake. Upon completion, the completion
status of the handshake is stored in xp_tls as flag bits and the reply to
the Null RPC is sent.
For the client, if CLSET_TLS has been set, a new TCP connection will
send the Null RPC with AUTH_TLS to initiate the handshake. The client
kernel RPC code will then block kernel I/O on the socket and do an upcall
to the rpctlscd(8) daemon to perform the handshake.
If the upcall is successful, ct_rcvstate will be maintained to indicate
if/when an upcall is being done.

If non-application data records are received, the code does an upcall to
the appropriate daemon, which will do a SSL_read() of 0 length to handle
the record(s).

When the socket is being shut down, upcalls are done to the daemons, so
that they can perform SSL_shutdown() calls to perform the "peer reset".

The rpctlssd(8) and rpctlscd(8) daemons require a patched version of the
openssl library and, as such, will not be committed to head at this time.

Although the changes done by this patch are fairly numerous, there should
be no semantics change to the kernel RPC at this time.
A future commit to the NFS code will optionally enable use of TLS for NFS.

Add the .h file that describes the operations for the rpctls_syscall.

This .h file will be used by the nfs-over-tls daemons to do the system
call that was added by r361599.