smb3: add missing flag definitions

SMB3 and 3.1.1 added two additional flags including
the priority mask.  Add them to our protocol definitions
in smb2pdu.h.  See MS-SMB2 2.2.1.2

Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Reviewed-by: Pavel Shilovsky <pshilov@microsoft.com>