[XFRM]: Extension for dynamic update of endpoint address(es)

Extend the XFRM framework so that endpoint address(es) in the XFRM
databases could be dynamically updated according to a request (MIGRATE
message) from user application. Target XFRM policy is first identified
by the selector in the MIGRATE message. Next, the endpoint addresses
of the matching templates and XFRM states are updated according to
the MIGRATE message.

Signed-off-by: Shinta Sugimoto <shinta.sugimoto@ericsson.com>
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>