osmo-bsc.cfg: change logging level nm info -> notice
Stop spamming logs with tons of DNM messages (state changes, events).
GSMTAP emits all these messages (including 'debug' ones) anyway.
Related: I9e60ea0968a44aa29753226626864ac9f4c1f8ab (osmo-ttcn3-hacks.git)
Change-Id: I49352b3caf9f6bbdd594cfcdea54038fc0eaa874
