ikev1: Don't use rekeyed CHILD_SAs for rekey detection

ikev1: Don't use rekeyed CHILD_SAs for rekey detection

An old (already rekeyed) CHILD_SA would get switched back into CHILD_REKEYING
state.  And we actually want to change the currently installed CHILD_SA to
that state and later CHILD_REKEYED and properly call e.g. child_rekey() and
not do this again with an old CHILD_SA.  Instead let's only check installed
or currently rekeying CHILD_SAs (in case of a rekey collision).  It's also
uncommon that there is a CHILD_SA in state CHILD_REKEYED but none in state
CHILD_INSTALLED or CHILD_REKEYING, which could happen if e.g. a peer deleted
and recreated a CHILD_SA after a rekeying.  But in that case we don't want
to treat the new CHILD_SA as rekeying (e.g. in regards to events on the bus).