If the original responder updates its list of additional addresses we
check if the remote endpoint changed and update the IPsec SAs if it did,
as we assume the original address became unavailable and the responder
already updated the SAs on its side.
If MOBIKE is enabled, we do have to switch to port 4500 with the
IKE_AUTH request, that is, before we know whether the other peer
actually supports MOBIKE or not.