[XFRM] netlink: Clear up some of the CONFIG_XFRM_SUB_POLICY ifdef mess

Moves all of the SUB_POLICY ifdefs related to the attribute size
calculation into a function.

Signed-off-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
1 file changed