The TCP PAWS fix for kernels with fast tick rates (r231767) changed the TCP
timestamp related stack variables to reference ms directly instead of ticks.
The h_ertt(4) Khelp module relies on TCP timestamp information in order to
calculate its enhanced RTT estimates, but was not updated as part of r231767.

Consequently, h_ertt has not been calculating correct RTT estimates since
r231767 was comitted, which in turn broke all delay-based congestion control
algorithms because they rely on the h_ertt RTT estimates.

Fix the breakage by switching h_ertt to use tcp_ts_getticks() in place of all
previous uses of the ticks variable. This ensures all timestamp related
variables in h_ertt use the same units as the TCP stack and therefore results in
meaningful comparisons and RTT estimate calculations.

Reported & tested by: Naeem Khademi (naeemk at ifi uio no)
Discussed with: bz
MFC after: 3 days