CIFS: Return -EAGAIN instead of -ENOTSOCK

When we attempt to send a packet while the demultiplex thread
is in the middle of cifs_reconnect() we may end up returning
-ENOTSOCK to upper layers. The intent here is to retry the request
once the TCP connection is up, so change it to return -EAGAIN
instead. The latter error code is retryable and the upper layers
will retry the request if needed.

Signed-off-by: Pavel Shilovsky <pshilov@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>