l1sap: l1sap_chan_act(): alloc DTX FSM only for TCH
l1sap: l1sap_chan_act(): alloc DTX FSM only for TCH

Change-Id: Ieb5728b7a9e7d7c58449deaa5a6c4d8755b6e213

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