osmux: Allocate rate counters during initialization of osmux conn

Let's not delay allocation of rate counters until the osmux conn is
fully enabled, since we may want to count stuff before that point in
time.

Fixes crash accessing null conn->osmux.ctrg in
MGCP_Test.TC_two_crcx_and_rtp_osmux_bidir.

Change-Id: Ic31d3567f4d24e628f8983d8362e5c7c2f66ec02
3 files changed