The following config could crash pfctl:
altq on igb0 fairq bandwidth 1Gb queue { qLink }
queue qLink fairq(default)
That happens because when we're parsing the parent queue (on igb0) it
doesn't have a parent, and the check in eval_pfqueue_fairq() checks
pa->parent rather than parent.
This was changed in eval_pfqueue_hfsc() in
1d34c9dac8624c5c315ae39ad3ae8e5879b23256, but not for fairq.
MFC after: 1 week
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