pf tests: Only log critical errors from scapy

See a26e895f3d803cc1f4ee1c2b33c61330998808b9. Silence these new tests as
well.

MFC after: 1 week
Sponsored by: Rubicon Communications, LLC ("Netgate")

(cherry picked from commit 9d0bc96ef8c0288c05a627b3961edd2da046c5c9)