ikev1: Prevent deadlock when checking for duplicate IKEv1 SAs

ikev1: Prevent deadlock when checking for duplicate IKEv1 SAs

Previously, the current segment was held while checking for duplicate
SAs, which requires acquiring all segments.  If multiple threads did this
concurrently this resulted in a deadlock as they couldn't acquire the
segments held by the other threads attempting to do the same.  With the
default configuration only one segment is used, which prevents the problem
as only one thread can check in an IKE SA concurrently.

Fixes: a064eaa8a63a ("Handling of initial contact")