Add enum gsm48_cause_coding from GSM 04.08 Section 10.5.4.11

Change-Id: I3d9c8e117ad19f70a3273650d7c0f8280d7bdb9a
diff --git a/include/osmocom/gsm/protocol/gsm_04_08.h b/include/osmocom/gsm/protocol/gsm_04_08.h
index 68ba650..0bb2dce 100644
--- a/include/osmocom/gsm/protocol/gsm_04_08.h
+++ b/include/osmocom/gsm/protocol/gsm_04_08.h
@@ -1387,6 +1387,14 @@
 	GSM48_SIGNAL_ALERT_OFF	= 0x4f,
 };
 
+/* Section 10.5.4.11 / Table 10.5.122 */
+enum gsm48_cause_coding {
+	GSM48_CAUSE_CODING_CCITT_Q931	= 0x00,
+	GSM48_CAUSE_CODING_RESERVED	= 0x01,
+	GSM48_CAUSE_CODING_NATIONAL	= 0x02,
+	GSM48_CAUSE_CODING_GSM		= 0x03,
+};
+
 enum gsm48_cause_loc {
 	GSM48_CAUSE_LOC_USER		= 0x00,
 	GSM48_CAUSE_LOC_PRN_S_LU	= 0x01,