[XFRM] IPV6: Add sort functions to combine templates/states for IPsec.

Add sort functions to combine templates/states for IPsec.
Think of outbound transformation order we should be careful with transport AH
which must be the last of all transport ones.

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