Reduce pf.conf parsing cost for configs that define N queues from O(N^2) to O(N)

The number of syscalls made during parsing of any config that
defines tables is also reduced, and incorrect warnings that HFSC
parent queue bandwidths were smaller than the sum of their child
bandwidths have been fixed.

Reviewed by: kp
MFC after: 1 week
Sponsored by: RG Nets
Differential Revision: https://reviews.freebsd.org/D18759