Update VPN event strings for the IKE lib update

With a recent update, the IKEv2 library exposed the internal
errors happening on the link. This had us realize one error
code was a little bit ill-named and the other can't be exposed
because the system doesn't know about it happening.

Update the name of the events for this.

Test: m
Change-Id: I228b8309acbb5f599b908633923b16cd09e9c0af