Optionally also kill states that match (i.e. are the NATed state or
opposite direction state entry for) the state we're killing.
See also https://redmine.pfsense.org/issues/8555
Submitted by: Steven Brown
Obtained from: https://github.com/pfsense/FreeBSD-src/pull/11/
MFC after: 1 week
Sponsored by: Rubicon Communications, LLC ("Netgate")