pf: allow MLD LR to be sent without state

Change PF behavior to allow MLD Listener Report packets to be sent
without needing a previously created state by MLD Listener Query. It
wasn't working because: (1) you might not have a previous MLD Listener
Query and (2) the addresses of the Query and Report don't match.

ok mikeb@, sashan@

MFC after: 1 day
Obtained From: OpenBSD, rzalamena <rzalamena@openbsd.org>, 5c526dbdb0f2
Sponsored by: Rubicon Communications, LLC ("Netgate")