IKEv1: don't include the KE payload in the IKE (ISAKMP?) exchange

Interop #1 omits KE from the request, which should promptly get
rejected by the responder.

Interop #2 includes KE, but then gets no KE back from the responder
which should cause the session to be aborted or retried.

However, since this is IKEv1, all that really matters is that this
doesn't dump core.