Fix TSC/BSIC handling bug and remove bts->tsc

This fixes a bug in the following circumstances:
* BSIC is set to 0 in the config file
* No TSC is explicitly specified at the BST level in the config file

In this case, we ended up using BSIC=0 and TSC=7, as TSC=7 is our
default initialization value.

The TSC of the CCCH/BCCH must always be the BCC, which is the lower 3
bits of the BSIC.  Having configuration options for both the BSIC _and_
the TSC at the BTS level therefore makes no sense, as it only adds ways
in which users can configure non-oprational configurations.  So we
remove the bts->tsc member, and keep only the ts->tsc members that allow
us to configure a timeslot-specific TSC that's different from the BTS
TSC (= BCC).
diff --git a/openbsc/src/libbsc/bsc_init.c b/openbsc/src/libbsc/bsc_init.c
index 9c19ec9..743f4c1 100644
--- a/openbsc/src/libbsc/bsc_init.c
+++ b/openbsc/src/libbsc/bsc_init.c
@@ -280,10 +280,10 @@
 	unsigned int i;
 
 	LOGP(DRSL, LOGL_NOTICE, "bootstrapping RSL for BTS/TRX (%u/%u) "
-		"on ARFCN %u using MCC=%u MNC=%u LAC=%u CID=%u BSIC=%u TSC=%u\n",
+		"on ARFCN %u using MCC=%u MNC=%u LAC=%u CID=%u BSIC=%u\n",
 		trx->bts->nr, trx->nr, trx->arfcn, bsc_gsmnet->country_code,
 		bsc_gsmnet->network_code, trx->bts->location_area_code,
-		trx->bts->cell_identity, trx->bts->bsic, trx->bts->tsc);
+		trx->bts->cell_identity, trx->bts->bsic);
 
 	if (trx->bts->type == GSM_BTS_TYPE_NOKIA_SITE) {
 		rsl_nokia_si_begin(trx);