CIFS: Add missed forcemand mount option

The 'forcemand' form of 'forcemandatorylock' mount option was missed
when the code moved to use the standard token parser. Return it back.

Also fix a comment style in the parser.

Signed-off-by: Pavel Shilovsky <piastry@etersoft.ru>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>