Merge branch 'consistent-reqid'

Checks if a trap policy exists when installing a CHILD_SA as responder,
reuse that reqid and keeping the trap untouched. This makes auto=route on
both sides more reliable.

In addition, we no prevent to refcount an existing policy if the reqid differs;
this should not happen anymore. We now can properly reject new CHILD_SAs in
such conflicts, instead of silently breaking an existing policy.