msc: Enable/disable osmux always based on test

Initially it was thought safe to only enable it since the osmux test was
at the end, but actually IU tests run after it, and those don't expect
osmux to be enabled.

This way we also always match osmo-msc osmux state with whatever the
test expects (and sets through f_init()).

Change-Id: I8fb48af7d37f1a2391a39c19f5ec5064cd5869d2
1 file changed