correct HTB rtable/HZ calculations

correct HTB rtable/HZ calculations

The HTB implementation in libnl uses units of microseconds in a number
of places where it seems TC is expecting time in units of ticks, which
causes actual rates much higher than requested.  Additionally, libnl
uses USER_HZ for calculating buffer and cbuffer sizes, which can
result in much larger buffers than necessary on systems with high
resolution timers.

Note that the TBF qdisc uses microseconds incorrectly in two spots as
well, I fixed this but did not test.