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_nokia_site.c b/openbsc/src/libbsc/bts_nokia_site.c
index 36e3fac..376a048 100644
--- a/openbsc/src/libbsc/bts_nokia_site.c
+++ b/openbsc/src/libbsc/bts_nokia_site.c
@@ -1724,6 +1724,7 @@
 
 	gsm_btsmodel_set_feature(&model_nokia_site, BTS_FEAT_HOPPING);
 	gsm_btsmodel_set_feature(&model_nokia_site, BTS_FEAT_HSCSD);
+	gsm_btsmodel_set_feature(&model_nokia_site, BTS_FEAT_MULTI_TSC);
 
 	osmo_signal_register_handler(SS_L_INPUT, inp_sig_cb, NULL);
 	osmo_signal_register_handler(SS_L_GLOBAL, gbl_sig_cb, NULL);