IKEv2 labeled IPsec with an acquire happening part way through the childless IKE exchange

- pluto configured to drop the first IKE_SA_INIT request
- initiate childless IKE SA in background
- while IKE SA is stalled, trigger acquire

The acquire should be put on the IKE's pending queue.  The retransmit
will then unstuck the entire process and establish both the IKE and
Child SAs.
