scheduler: use RSL_CHAN_NR_MASK in trx_sched_set_lchan()
scheduler: use RSL_CHAN_NR_MASK in trx_sched_set_lchan()

Change-Id: I3dd2c90f510444cda38516bd9a1a207877bebadc

osmocom/osmo-bts,osmocom/osmo-bts,osmocom/osmo-bts