xfrm: Simplify SA looking up when using wildcard source

__xfrm4/6_state_addr_check is a four steps check, all we need to do
is checking whether the destination address match when looking SA
using wildcard source address. Passing saddr from flow is worst option,
as the checking needs to reach the fourth step while actually only
one time checking will do the work.

So, simplify this process by only checking destination address when
using wildcard source address for looking up SAs.

Signed-off-by: Fan Du <fan.du@windriver.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>