pf tests: ensure that traceroutes using ICMP work

PR: 280701
Approved by: re (cperciva)
MFC after: 1 week
Sponsored by: Rubicon Communications, LLC ("Netgate")

(cherry picked from commit 34063cb714602972b6d985ad747fc8f66a8daae1)
(cherry picked from commit 7024e1066d5aba76dbbc85eb191357da7d32c619)