[PATCH] bsc,nitb: Store rf_ctrl in the net structure in osmo-nitb.

Hi all, Prevent crash introduced in the a9fae1ae commit. Call "show network" in the NITB VTY without any BTS connected to reproduce the crash. Before it was stored in a local variable, but accessed from a net structure in the msc_signal_handler(). -- Regards, Alexander Chemeris. CEO, Fairwaves, Inc. / ООО УмРадио https://fairwaves.co