trxcon/l1sched: pre-populate MR cache during lchan allocation
Instead of checking if the MR cache is populated in prim_compose_mr() and populating it there, let's do this during lchan allocation. Take a chance to move lchan allocation logic into its own function.
trxcon/fsm: handle_dch_est_req(): do not reset the scheduler
Calling l1sched_reset() results in resetting the UL SACCH cache, that may have been populated prior to sending L1CTL_DM_EST_REQ. Instead, do what the comment says - call l1sched_del_all_ts().
