Do not manipulate read queue directly

Protocol modules should not manupulate the read queue directly,
but always access it via the functions created for that purpose.

server/modules/protocol/MySQL/mysql_common.c

@@ -981,8 +981,7 @@ bool read_complete_packet(DCB *dcb, GWBUF **readbuf)
         {
             /** Store any extra data in the DCB's readqueue */
 
-            dcb->dcb_readqueue = gwbuf_append(dcb->dcb_readqueue, localbuf);
-
+            dcb_readq_append(dcb, localbuf);
         }
     }