features: move bts feature related functionality to libosmocore

osmo-bsc and osmo-bts share enums and value strings to describe
feature data that is exchanged via OML (manufacturer id) on startup.
Also the functions to set and get the respecitive bits in the feature
bitvectors are in osmo-bsc and osmo-bts. This is a code duplication
and should be resolved.

- add enum osmo_bts_features (replaces enum gsm_bts_features)
- add osmo_bts_features_descs (replaces gsm_bts_features_descs)
- add osmo_bts_set_feature (replaces gsm_btsmodel_set_feature)
- add osmo_bts_has_feature (replaces gsm_btsmodel_has_feature)

Change-Id: Id0c35aef11aa49aa40abe7deef1f9dbd12210776
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index 0a1c0c6..b903504 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -262,6 +262,8 @@
 gsm48_mcc_mnc_from_bcd;
 gsm48_generate_lai2;
 gsm48_decode_lai2;
+osmo_bts_features_descs;
+osmo_bts_feature_name;
 osmo_plmn_to_bcd;
 osmo_plmn_from_bcd;
 osmo_mcc_name;