pf: be less strict about icmp state checking for sloppy state tracking

Sloppy state tracking renders ICMP direction check useless
and harmful as we might see only half of the connection in
the asymmetric setups but ignore the state match. The bug
was reported and fix was verified by Insan Praja <insan ()
ims-solusi ! com>. Thanks! OK mcbride, henning

MFC after: 1 week
Obtained from: OpenBSD, mikeb <mikeb@openbsd.org>, 538596657140
Sponsored by: Rubicon Communications, LLC ("Netgate")