smb: common: add header guards to fs/smb/common/smb2status.h

smb: common: add header guards to fs/smb/common/smb2status.h

This will allow it to be included multiple times without problems,
that's needed for the smbdirect move to common code.

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: 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>