gsm: gsm_utils: Fix return type of API ms_class_gmsk_dbm() and add unit tests
Only known user of API is in osmocom-bb and it compiles fine after the
change.
Related: OS#4244
Change-Id: Ia10345008b3aca50b30482ef3b852b03eca71995
diff --git a/src/gsm/gsm_utils.c b/src/gsm/gsm_utils.c
index 365920f..ae77a9d 100644
--- a/src/gsm/gsm_utils.c
+++ b/src/gsm/gsm_utils.c
@@ -501,8 +501,8 @@
/*! Convert power class to dBm according to GSM TS 05.05
* \param[in] band GSM frequency band
* \param[in] class GSM power class
- * \returns maximum transmit power of power class in dBm */
-unsigned int ms_class_gmsk_dbm(enum gsm_band band, int class)
+ * \returns maximum transmit power of power class in dBm, negative on error */
+int ms_class_gmsk_dbm(enum gsm_band band, int class)
{
switch (band) {
case GSM_BAND_450: