hodec2: fix congestion oscillation bug

When evenly distributing congestion across cells, count the number of
occupied lchans surpassing congestion, and not the overall number of
free lchans -- which disregards congestion thresholds.

Fix the bugs shown by
 test_congestion_no_oscillation.ho_vty
 test_balance_congestion_tchf_tchh.ho_vty

This implements a simple calculation for congestion load by counting
lchans in use above congestion. An improvement of this calculation
using percent follows in I55234c6c99eb02ceee52be0d7388bea14304930f.

Related: SYS#5259
Change-Id: Icb373dc6bfc9819446db5e96f71921781fe2026d
4 files changed