bts/osmo-bts.cfg: reduce OML logging verbosity, degrade to notice

Average size of osmo-bts.log after running ttcn3-bts-test is ~178 MB,
and more than 52% (!) of it is the OML logging messages.  Other than
making the logfile bigger, bursts of OML messages make it really hard
to follow the output of osmo-bts when running tests natively.

Change-Id: Ib5346a3ca42917169e195f905472ccea7579e5eb
1 file changed