Do not expect all BTSs support TSC != BCC

We introduce a new feature indicating if the given BTS model
supports a TSC that is different from the BCC (lower 3 bits of BSIC).
diff --git a/openbsc/src/libbsc/bts_sysmobts.c b/openbsc/src/libbsc/bts_sysmobts.c
index 754e277..e1bf661 100644
--- a/openbsc/src/libbsc/bts_sysmobts.c
+++ b/openbsc/src/libbsc/bts_sysmobts.c
@@ -51,6 +51,7 @@
 	model_sysmobts.features.data = &model_sysmobts._features_data[0];
 	model_sysmobts.features.data_len =
 				sizeof(model_sysmobts._features_data);
+	memset(model_sysmobts.features.data, 0, sizeof(model_sysmobts.features.data_len));
 
 	gsm_btsmodel_set_feature(&model_sysmobts, BTS_FEAT_GPRS);
 	gsm_btsmodel_set_feature(&model_sysmobts, BTS_FEAT_EGPRS);