MFC: r317906
Fix the client side krpc from doing TCP reconnects for ERESTART from sosend().

When sosend() replies ERESTART in the client side krpc, it indicates that
the RPC message hasn't yet been sent and that the send queue is full or
locked while a signal is posted for the process.
Without this patch, this would result in a RPC_CANTSEND reply from
clnt_vc_call(), which would cause clnt_reconnect_call() to create a new
TCP transport connection. For most NFS servers, this wasn't a serious problem,
although it did imply retries of outstanding RPCs, which could possibly
have missed the DRC.
For an NFSv4.1 mount to AmazonEFS, this caused a serious problem, since
AmazonEFS often didn't retain the NFSv4.1 session and would reply with
NFS4ERR_BAD_SESSION. This implies to the client a crash/reboot which
requires open/lock state recovery.

Three options were considered to fix this:
- Return the ERESTART all the way up to the system call boundary and then
have the system call redone. This is fraught with risk, due to convoluted
code paths, asynchronous I/O RPCs etc. cperciva@ worked on this, but it
is still a work in prgress and may not be feasible.
- Set SB_NOINTR for the socket buffer. This fixes the problem, but makes
the sosend() completely non interruptible, which kib@ considered
inappropriate. It also would break forced dismount when a thread
was blocked in sosend().
- Modify the retry loop in clnt_vc_call(), so that it loops for this case
for up to 15sec. Testing showed that the sosend() usually succeeded by
the 2nd retry. The extreme case observed was 111 loop iterations, or
about 100msec of delay.
This third alternative is what is implemented in this patch, since the
change is:
- localized
- straightforward
- forced dismount is not broken by it.

This patch has been tested by cperciva@ extensively against AmazonEFS.

MFC: r316694
Fix a crash during unmount of an NFSv4.1 mount.

Larry Rosenman reported a crash on freebsd-current@ which was caused by
a premature release of the krpc backchannel socket structure.
I believe this was caused by a race between the SVC_RELEASE() in clnt_vc.c
and the xprt_unregister() in the higher layer (clnt_rc.c), which tried
to lock the mutex in the xprt structure and crashed.
This patch fixes this by removing the xprt_unregister() in the clnt_vc
layer and allowing this to always be done by the clnt_rc (higher reconnect
layer).

MFstable/11 r303691:

MFC r302550,r302551,r302552,r302553:

r302550:

Deobfuscate cleanup path in clnt_dg_create(..)

Similar to r300836 and r301800, cl and cu will always be non-NULL as they're
allocated using the mem_alloc routines, which always use
`malloc(..., M_WAITOK)`.

Deobfuscating the cleanup path fixes a leak where if cl was NULL and
cu was not, cu would not be free'd, and also removes a duplicate test for
cl not being NULL.

CID: 1007033, 1007344

r302551:

Deobfuscate cleanup path in clnt_vc_create(..)

Similar to r300836, r301800, and r302550, cl and ct will always
be non-NULL as they're allocated using the mem_alloc routines,
which always use `malloc(..., M_WAITOK)`.

CID: 1007342

r302552:

Convert `svc_xprt_alloc(..)` and `svc_xprt_free(..)`'s prototypes to
ANSI C style prototypes

r302553:

Don't test for xpt not being NULL before calling svc_xprt_free(..)

svc_xprt_alloc(..) will always return initialized memory as it uses
mem_alloc(..) under the covers, which uses malloc(.., M_WAITOK, ..).

CID: 1007341

MFC: r265238, r265240

Properly free resources in case of error.

CID: 1007032
Found with: Coverity Prevent(tm)

MFC r258578, r258580, r258581 (by hrs):
Replace Sun RPC license in TI-RPC library with a 3-clause BSD license
with the explicit permissions.

MFC r259842:

Remove some unused static const strings under sys/rpc, which have never
been used since the initial commit (r177633).

MFC r259843:

Move a static const variable to the #if 0 part where it is only used.
(Note the #if 0 part has been inactive since the initial commit,
r177633, so maybe it should be removed altogether).

MFC: r265238, r265240

Properly free resources in case of error.

CID: 1007032
Found with: Coverity Prevent(tm)

MFC r258578, r258580, r258581 (by hrs):
Replace Sun RPC license in TI-RPC library with a 3-clause BSD license
with the explicit permissions.

MFC r259842:

Remove some unused static const strings under sys/rpc, which have never
been used since the initial commit (r177633).

MFC r259843:

Move a static const variable to the #if 0 part where it is only used.
(Note the #if 0 part has been inactive since the initial commit,
r177633, so maybe it should be removed altogether).