gsm_08_08: gsm0808_permitted_speech does not have value strings

enum gsm0808_permitted_speech does not have any value strings. Lets
add value strings to make debugging easier.

Change-Id: I5b5612a5df2758b0137a34c17f7c8c2b3f07c806
diff --git a/include/osmocom/gsm/protocol/gsm_08_08.h b/include/osmocom/gsm/protocol/gsm_08_08.h
index db5f7fa..bd5705f 100644
--- a/include/osmocom/gsm/protocol/gsm_08_08.h
+++ b/include/osmocom/gsm/protocol/gsm_08_08.h
@@ -430,6 +430,10 @@
 	GSM0808_PERM_HR6	= 0x45, /*!< OHR AMR */
 };
 
+extern const struct value_string gsm0808_permitted_speech_names[];
+static inline const char *gsm0808_permitted_speech_name(enum gsm0808_permitted_speech val)
+{ return get_value_string(gsm0808_permitted_speech_names, val); }
+
 /*! 3GPP TS 48.008, 3.2.2.103 Speech Codec Type */
 enum gsm0808_speech_codec_type {
 	GSM0808_SCT_FR1	= 0x0, /*!< GSM FR */