Adds a missing constant.

src/org/jitsi/service/neomedia/codec/Constants.java

@@ -81,6 +81,11 @@ public class Constants
      */
     public static final String ILBC_RTP = "ilbc/rtp";
 
+    /**
+     * The OPUS constant.
+     */
+    public static final String OPUS = "opus";
+
     /**
      * The OPUS/RTP constant.
      */