altq: Increase maximum number of CBQ and HFSC classes

In some configurations we need more classes than ALTQ supports by
default. Increase the maximum number of classes we allow.
This will only cost us a comparatively trivial amount of memory, so
there's little reason not to do so.

If ever we find we want even more we may want to consider turning these
defines into a tunable, but for now do the easy thing.

Reviewed by: donner@
MFC after: 2 weeks
Sponsored by: Rubicon Communications, LLC ("Netgate")
Differential Revision: https://reviews.freebsd.org/D29034