smb: client: make use of smbdirect_socket.mr_io

smb: client: make use of smbdirect_socket.mr_io

Now struct smbd_connection only contains struct smbdirect_socket,
this is an important step towards having common functions as well.

Cc: Steve French <smfrench@gmail.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Long Li <longli@microsoft.com>
Cc: linux-cifs@vger.kernel.org
Cc: samba-technical@lists.samba.org
Acked-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Steve French <stfrench@microsoft.com>