pf: Fix tests broken by enabling inet-local filtering

Summary:
Three of the pf dummynet tests were using filter rules which matched
both the intended epair interface as well as lo0 which now receives
PFIL_OUT events for messages delivered to the local network stack (if
enabled). This commit changes the rules to match only for the expected
epair interface.

PR: 268717
Reviewed-by: kp
MFC-after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D40393