IKEv2 streams with exchanges perfectly interleaved

connection ends up with IKE SA from one end and Child SA from peer

First:

    west initiates IKE-I#1
    east responds with IKE-R#2
    west initiates CHILD-I#3 using IKE-I#1
    east responds with CHILD-R#4 using IKE-R#2

so everything is established.  Then:

    east deletes IKE-R#2
