[PATCH 0/4][SRU][focal:linux] NFSv4.1: Don't rebind to the same source port when reconnecting to the server

[Tim Gardner]

BugLink: https://bugs.launchpad.net/bugs/1997488

SRU Justification

Microsoft asked for this backport complaining that, 
"NFS 4.1 mounts on AKS are reusing the same source port when a reconnect needs to happen".

Patches 1-3 are scaffolding in order to provide a clean cherrypick for patch 4.
This issue looks applicable to the generic kernel.

[Impact]

NFSv2, v3 and NFSv4 servers often have duplicate replay caches that look
at the source port when deciding whether or not an RPC call is a replay
of a previous call. This requires clients to perform strange TCP gymnastics
in order to ensure that when they reconnect to the server, they bind
to the same source port.

NFSv4.1 and NFSv4.2 have sessions that provide proper replay semantics,
that do not look at the source port of the connection. This patch therefore
ensures they can ignore the rebind requirement.

[Where things could go wrong]

NFS reconnects may erroneously fail.

[Other Info]

SF: #00345839