port arfcn range encode support from osmo-bsc

As part of fixing issue OS#3075, we want to migrate support
for encoding system information from osmo-bsc to libosmocore.

This change ports one of the prerequisites for doing so:
osmo-bsc code for range-encoding ARFCNs, including tests.

An osmo_gsm48_ prefix has been prepended to public symbols in
order to avoid clashes with existing symbols in osmo-bsc code.

Change-Id: Ia220764fba451be5e975ae7c5eefb1a25ac2bf2c
Related: OS#3075
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index cdcbcc9..922ac01 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -518,6 +518,15 @@
 osmo_apn_to_str;
 osmo_apn_from_str;
 
+osmo_gsm48_range_enc_determine_range;
+osmo_gsm48_range_enc_arfcns;
+osmo_gsm48_range_enc_find_index;
+osmo_gsm48_range_enc_filter_arfcns;
+osmo_gsm48_range_enc_128;
+osmo_gsm48_range_enc_256;
+osmo_gsm48_range_enc_512;
+osmo_gsm48_range_enc_1024;
+
 osmo_gsup_encode;
 osmo_gsup_decode;
 osmo_gsup_message_type_names;