gsm_ts_release(): Make sure pchan{,is_want} is reset to NONE
gsm_ts_release(): Make sure pchan{,is_want} is reset to NONE

Let's make sure all ts->pchan* related data is reset when we release the
TS. This is important for pchan_is, since in bts-trx upon shutdown
finish the PDCH lchan of a osmo dyn TS is set to
lchan->state=LCHAN_S_NONE, and as a result when the PCU tries to release
it by means of PCUIF act_req later, it may be ignored since the lchan is
already in erased state.

Related: SYS#4971
Change-Id: Ic7c34c0de23101ce094ffd03e00b4d2f6a551152

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