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.
MFC after: 2 weeks
Sponsored by: Rubicon Communications, LLC ("Netgate")