NFSv4.1: Use seqid returned by EXCHANGE_ID after state migration

NFSv4.1: Use seqid returned by EXCHANGE_ID after state migration

Transparent State Migration copies a client's lease state from the
server where a filesystem used to reside to the server where it now
resides. When an NFSv4.1 client first contacts that destination
server, it uses EXCHANGE_ID to detect trunking relationships.

The lease that was copied there is returned to that client, but the
destination server sets EXCHGID4_FLAG_CONFIRMED_R when replying to
the client. This is because the lease was confirmed on the source
server (before it was copied).

Normally, when CONFIRMED_R is set, a client purges the lease and
creates a new one. However, that throws away the entire benefit of
Transparent State Migration.

Therefore, the client must use the contrived slot sequence value
returned by the destination server for its first CREATE_SESSION
operation after a Transparent State Migration.

Orabug: 25802443
Reported-by: Xuan Qi <xuan.qi@oracle.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
(hand picked mainline 838edb9 NFSv4.1: Use seqid returned ...)
Signed-off-by: Manjunath Patil <manjunath.b.patil@oracle.com>