xfrm: Restrict SA direction attribute to specific netlink message types

Reject the usage of the SA_DIR attribute in xfrm netlink messages when
it's not applicable. This ensures that SA_DIR is only accepted for
certain message types (NEWSA, UPDSA, and ALLOCSPI)

Signed-off-by: Antony Antony <antony.antony@secunet.com>
Reviewed-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>