pf: try to lookup the icmp state based on a correct packet descriptor

Approved by: so
Security: FreeBSD-EN-24:16.pf
MFC after: 1 week
Obtained from: OpenBSD, mikeb <mikeb@openbsd.org>, e467ea25dcd3
Sponsored by: Rubicon Communications, LLC ("Netgate")

(cherry picked from commit b8cd169efa6ac0899b4998898129765ae5c685a6)
(cherry picked from commit f40b0e735177b25ce67fb488a93834168f4c16e1)