cifs: smbd: Return -EAGAIN when transport is reconnecting

commit 4357d45f50e58672e1d17648d792f27df01dfccd upstream.

During reconnecting, the transport may have already been destroyed and is in
the process being reconnected. In this case, return -EAGAIN to not fail and
to retry this I/O.

Signed-off-by: Long Li <longli@microsoft.com>
Cc: stable@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>