smb: smbdirect: add smbdirect_socket.h

This abstracts the common smbdirect layer.

Currently with just a few things in it,
but that will change over time until everything is
in common.

Will be used in client and server in the next commits

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