Merge branch 'ikev1-cache-informational'
With these changes an INFORMATIONAL message (e.g. with an INITIAL_CONTACT
notify) that arrives while a responder is waiting for the last Aggressive
Mode request gets queued and delivered later. Previously such messages
caused the IKE_SA to fail as some tasks waiting for the last AM message
fail when trying to handle the INFORMATIONAL message. Therefore, all
other messages, such as TRANSACTION and QUICK_MODE requests, are now
dropped until AM is complete. These don't have to be cached as they get
retransmitted by the other peer.
Fixes #1130.