Move T3172 T_defs_bts->T_defs_pcu to have it configurable in VTY

The timers in T_defs_bts are actually set by BTS over PCUIF. That's not
the case for T3172, hence let's move it to T_defs_pcu so it can be
configured over VTY.

Change-Id: If24191b2305007aa5be5b551c913738a97597c77
diff --git a/src/tbf_ul_ass_fsm.c b/src/tbf_ul_ass_fsm.c
index ef75360..90fe828 100644
--- a/src/tbf_ul_ass_fsm.c
+++ b/src/tbf_ul_ass_fsm.c
@@ -64,7 +64,7 @@
 	bitvec_unhex(packet_access_rej, DUMMY_VEC);
 
 	write_packet_access_reject(packet_access_rej, ms_tlli(ms),
-				   osmo_tdef_get(ms->bts->T_defs_bts, 3172, OSMO_TDEF_MS, -1));
+				   osmo_tdef_get(ms->bts->pcu->T_defs, 3172, OSMO_TDEF_MS, -1));
 
 	bts_do_rate_ctr_inc(ms->bts, CTR_PKT_ACCESS_REJ);