[XFRM] STATE: Use destination address for src hash.

Src hash is introduced for Mobile IPv6 route optimization usage.
On current kenrel code it is calculated with source address only.
It results we uses the same hash value for outbound state (when
the node has only one address for Mobile IPv6).
This patch use also destination address as peer information for
src hash to be dispersed.

Signed-off-by: Masahide NAKAMURA <nakam@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>