gsm0808: Implement helper functions for CONFUSION BSSMAP message decoding.

Also add a test for an actual CONFUSION message parsing.

Change-Id: If8afd2d096fb66c6c2f255a08fc1129de3d09cec
diff --git a/include/osmocom/gsm/gsm0808.h b/include/osmocom/gsm/gsm0808.h
index 5a33f60..34cec3c 100644
--- a/include/osmocom/gsm/gsm0808.h
+++ b/include/osmocom/gsm/gsm0808.h
@@ -319,6 +319,9 @@
  * \returns Cause value */
 enum gsm0808_cause gsm0808_get_cause(const struct tlv_parsed *tp);
 
+const char *gsm0808_diagnostics_octet_location_str(uint8_t pointer);
+const char *gsm0808_diagnostics_bit_location_str(uint8_t bit_pointer);
+
 extern const struct value_string gsm0808_lcls_config_names[];
 extern const struct value_string gsm0808_lcls_control_names[];
 extern const struct value_string gsm0808_lcls_status_names[];