MFC: r291527
Add kernel support to the NFS server for the "-manage-gids"
option that will be added to the nfsuserd daemon in a future
commit. It modifies the cache used by NFSv4 for name<-->id
translation (both username/uid and group/gid) to support this.
When "-manage-gids" is set, the server looks up each uid
for the RPC and uses the list of groups cached in the server
instead of the list of groups provided in the RPC request.
The cached group list is acquired for the cache by the nfsuserd
daemon via getgrouplist(3).
This avoids the 16 groups limit for the list in the RPC request.
Since the cache is now used for every RPC when "-manage-gids"
is enabled, the code also modifies the cache to use a separate
mutex for each hash list instead of a single global mutex.

Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Add an nfssvc() option to the kernel for the new NFS client
which dumps out the actual options being used by an NFS mount.
This will be used to implement a "-m" option for nfsstat(1).

Reviewed by: alfred
MFC after: 2 weeks

Add two new options to the nfssvc(2) syscall that allow
processes running as root to suspend/resume execution
of the kernel nfsd threads. An earlier version of this
patch was tested by Vincent Hoffman (vince at unsane.co.uk)
and John Hickey (jh at deterlab.net).

Reviewed by: kib
MFC after: 2 weeks

Add kernel support for NFSSVC_ZEROCLTSTATS and NFSSVC_ZEROSRVSTATS
so that they can be used by nfsstat(1) to implement the "-z" option
for the new NFS subsystem.

MFC after: 2 weeks

Revert r221306, since NFSSVC_ZEROSTATS zero'd both client and
server stats, when separate modifiers for NFSSVC_GETSTATS for
each of client and server stats is what it required by nfsstat(1).

Add the kernel support needed to zero out the nfsstats
structure for the new NFS subsystem. This will be used
by nfsstats.c to implement the "-z" option.

MFC after: 2 weeks

Modify the experimental NFSv4 server so that it posts a SIGUSR2
signal to the master nfsd daemon whenever the stable restart
file has been modified. This will allow the master nfsd daemon
to maintain an up to date backup copy of the file. This is
enabled via the nfssvc() syscall, so that older nfsd daemons
will not be signaled.

Reviewed by: jhb
MFC after: 1 week

Adding sys/nfs/nfssvc.h and sys/nfs/nfs_nfssvc.c in preparation for
sharing of the nfssvc() system call between nfsserver and the nfsv4
server. Building of nfs_nfssvc.c will be committed later, at the time
the .c files in sys/nfsserver are updated. To do so now would result in
nfssvc() multiply defined.

Submitted by: rmacklem
Reviewed by: dfr
Approved by: kib (mentor)