IKE exchange crosses, initiator conswitches peer's child leaving local ike hanging

each end has two connections that can share their IKE SA

- WEST sends "a":IKE_SA_INIT to EAST
  - creates IKE SA #1
  - initiator sets "a".{routing,negotiating}_ike_sa to #1

- EAST sends "b":IKE_SA_INIT to WEST

- WEST responds to EAST'S "b":IKE_SA_INIT
  - creates IKE_SA #2 using connection "a"
  - responder leaves "a".{routing,negotiating}_ike_sa et.al. untouched

- EAST sends "b":IKE_AUTH to WEST

- WEST responds to EAST's "b":IKE_AUTH
  IKE
  - establishes IKE SA #2
  - sets "a".{established,negotiating}_ike_sa #2
  - leaves "a".routing_sa set to #1
  Child:
  - creates Child SA #3
  - connswitches Child SA #3 to "b"
  - establishes Child SA #3
  - sets "b".{routing,negotiating,established}_child_sa to #3

- WEST retransmits "a":IKE_SA_INIT #1 to EAST
  - sees .established_ike_sa(?) is #2 stops negotiation
    "tun-out-1" #1: suppressing retransmit because IKE SA was superseded #2; drop this negotiation
  - tries to revive:
    EXPECTATION FAILED: "a" #1: revival: skipping, .negotiating_ike_sa #2 is is not us

ref github #1989
