smb: smbdirect: introduce and use include/linux/smbdirect.h

smb: smbdirect: introduce and use include/linux/smbdirect.h

This makes it easier to rebuild cifs.ko and ksmbd.ko against
a running kernel.

Suggested-by: Christoph Hellwig <hch@infradead.org>
Link: https://lore.kernel.org/linux-cifs/aehrPuY60VMcYGU8@infradead.org/
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: Christoph Hellwig <hch@infradead.org>
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>