osmo-bts-trx: fix lchan deactivation
osmo-bts-trx: fix lchan deactivation

Use chan_nr for deactivating lchan instead of lchan->nr: chan_nr is the
RSL Channel Number IE value, a bitfield aggregation of lchan type
bits (cbits) and lchan number (lowest three bits). The error was
introduced in 36153239bfd0b633c4d259a9de0a759f41197a2b.

Change-Id: I6dd7060422ab9d18743c1ff2ab419e3e7299d74d

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