XFRM: Mobile IPv6 route optimization support.

XFRM: Mobile IPv6 route optimization support.

To support Mobile IPv6 RO, the following extension is included:
o Use XFRM_MODE_XXX macro instead of magic number
o New attribute option for all state: source address for
  deleting or getting message
o New attribute options for RO: care-of address, last-used timestamp
  and wild-receive flag

Note:
Flush command like `ip xfrm state flush` is to remove all XFRM state.
It has been effected for IPsec SAD but with this patch it flushes both
IPsec SAD and Mobile IPv6 RO states.
To make only IPsec SA flush, it is recommanded to specify each XFRM
protocol like below:
 `ip x s f proto esp ; ip x s f proto ah ; ip x s f proto comp`

Signed-off-by: Masahide NAKAMURA <nakam@linux-ipv6.org>
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>