[IPSEC]: Replace x->type->{local,remote}_addr with flags

The functions local_addr and remote_addr are more than what they're
needed for.  The same thing can be done easily with flags on the type
object.  This patch does that and simplifies the wrapper functions in
xfrm6_policy accordingly.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>