[BSC] introduce the concept of 'BTS features'

We can then check if a bts supports a certain feature or not.
diff --git a/openbsc/src/bts_siemens_bs11.c b/openbsc/src/bts_siemens_bs11.c
index c966825..3d4ddda 100644
--- a/openbsc/src/bts_siemens_bs11.c
+++ b/openbsc/src/bts_siemens_bs11.c
@@ -62,5 +62,11 @@
 
 int bts_model_bs11_init(void)
 {
+	model_bs11.features.data = &model_bs11._features_data;
+	model_bs11.features.data_len = sizeof(model_bs11._features_data);
+
+	gsm_btsmodel_set_feature(&model_bs11, BTS_FEAT_HOPPING);
+	gsm_btsmodel_set_feature(&model_bs11, BTS_FEAT_HSCSD);
+
 	return gsm_bts_model_register(&model_bs11);
 }