pf: Fix tests broken by enabling inet-local filtering

[dfr]

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

Test Plan

kyua test -k /usr/tests/Kyuafile sys/netpfil/common/dummynet

[kp]

That's a little unexpected, but given that it'd only happen when the (currently) non-default hook is enabled that fine.
It's also pretty common for users to have a 'set skip on lo' rule, which I assume would prevent this too.

[dfr]

I actually tried adding a 'skip on lo' rule to these tests but for some reason the dnpipe rules still matched. Possibly i had the rule ordering wrong or needed 'skip quick on lo' instead. In real-world scenarios, I don't think this is likely to be a widespread problem and I still would like to move forward with D40373.