xfrm: add XFRMA_REPLAY_VAL attribute to SA messages

After this commit, the attribute XFRMA_REPLAY_VAL is added when no ESN replay
value is defined. Thus sequence number values are always notified to userspace.

Signed-off-by: dingzhi <zhi.ding@6wind.com>
Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>