add some clarification

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@9238 d0543943-73ff-0310-b7d9-9358b9ac24b2

src/switch_channel.c

@@ -101,6 +101,7 @@ static struct switch_cause_table CAUSE_CHART[] = {
 	{"USER_CHALLENGE", SWITCH_CAUSE_USER_CHALLENGE},
 	{"MEDIA_TIMEOUT", SWITCH_CAUSE_MEDIA_TIMEOUT},
 	{"PICKED_OFF", SWITCH_CAUSE_PICKED_OFF},
+	{"USER_NOT_REGISTERED", SWITCH_CAUSE_USER_NOT_REGISTERED},
 	{NULL, 0}
 };