[XFRM] IPV6: Support Mobile IPv6 extension headers sorting.

Support Mobile IPv6 extension headers sorting for two transformation policies.
Mobile IPv6 extension headers should be placed after IPsec
transport mode, but before transport AH when outbound.

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>