Export names for gsm_chan_t and gsm48_chan_mode

This can be used with get_value_string() to improve debugging output.
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index a6908a2..a3e4e14 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -144,6 +144,8 @@
 gsm48_mi_type_name;
 gsm48_mcc_mnc_to_bcd;
 gsm48_mcc_mnc_from_bcd;
+gsm48_chan_mode_names;
+gsm_chan_t_names;
 
 gsm_7bit_decode;
 gsm_7bit_decode_ussd;