cifs: smbd: avoid reconnect lockup

During transport reconnect, other processes may have registered memory
and blocked on transport. This creates a deadlock situation because the
transport resources can't be freed, and reconnect is blocked.

Fix this by returning to upper layer on timeout. Before returning,
transport status is set to reconnecting so other processes will release
memory registration resources.

Upper layer will retry the reconnect. This is not in fast I/O path so
setting the timeout to 5 seconds.

Signed-off-by: Long Li <longli@microsoft.com>
Signed-off-by: Steve French <smfrench@gmail.com>
Reviewed-by: Ronnie Sahlberg <lsahlber@redhat.com>
CC: Stable <stable@vger.kernel.org>