dummynet tests: Add CoDel/PIE masked and reconfiguration cases

[w453y.me_gmail.com]

Summary

aqm_masked configures CoDel and PIE on pipes with a mask and CoDel on
a queue of a masked WF2Q+ scheduler. aqm_reconfig changes the
parameters and the AQM of a pipe and of two queues (one masked) while
ping keeps an instance alive, and checks that the AQM is still there
and that traffic still passes afterwards.

PR: 298731
Signed-off-by: Abdul Wasey <[e-mail]>

Test Plan

• aqm_masked and aqm_reconfig (ipfw and pf variants) fail 4/4 on stock, at the first AQM check, and pass with the first two reviews; the whole dummynet suite passes 22/22. The suite needs if_bridge loaded and net.inet.ip.fw.default_to_accept=1, like the existing cases.