gsm: Add method to find ARFCN based on frequency

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index 3373888..b2278f1 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -137,6 +137,7 @@
 
 gsm_arfcn2band;
 gsm_arfcn2freq10;
+gsm_freq102arfcn;
 gsm_band_name;
 gsm_band_parse;
 gsm_fn2gsmtime;