bsc: Rename s/use_osmux/use_osmux_cn/

That config is used to control the use of osmux between BSC<->MSC. Since
we'll add support for Osmux in BTS<->BSC, we want to test that in a
separate way. Let's rename it so that we can add a "use_osmux_bts" later
on.

Change-Id: I3bde4e6772c18043dd763d7747b5dbe40e0da3b8
3 files changed