patch that fixes server reboot recovery problems for the NFSV4.1 client for review

[Rick Macklem]

There is now a patch at:
   https://reviews.freebsd.org/D8745
that fixes assorted problems w.r.t. the NFSv4.1 client doing recovery after a
server reboot (reply of NFS4ERR_BAD_SESSION to an RPC).

Please test/review/comment on it.
It is fairly large, but I do not believe it will affect the NFS client in other ways
than the NFSv4.1 recovery. This recovery seldom happens for most servers,
but it appears that AmazonEFS is an exception.

Thanks, rick