Add Osmux log category

Change-Id: Ia75de7965c39f3f84164a25584d901dbdd43f10f
diff --git a/include/osmocom/mgcp/debug.h b/include/osmocom/mgcp/debug.h
index 7044c1e..f7d47d6 100644
--- a/include/osmocom/mgcp/debug.h
+++ b/include/osmocom/mgcp/debug.h
@@ -30,6 +30,7 @@
 enum {
 	DRTP,
 	DE1,
+	DOSMUX,
 	Debug_LastEntry,
 };