smb: smbdirect: add smbdirect.h with public structures

smb: smbdirect: add smbdirect.h with public structures

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>