* gsm_bts_send_c0_power_red(): check if BTS is online first
* bts: st_op_enabled_on_enter(): resume C0 power reduction
* bootstrap_rsl(): cosmetic: cache trx->bts and use it directly
* struct gsm_bts_model: rename power_ctrl_{set->send}_c0_power_red
* bts_is_online(): make the BTS pointer const, return bool