OS-7088 cyclics corked on overlay socket with full queue

@@ -1105,11 +1105,12 @@
 
 out:
         mutex_enter(&odd->odd_lock);
         overlay_io_done(odd, OVERLAY_F_IN_TX);
         mutex_exit(&odd->odd_lock);
-        return (mp_chain);
+        freemsgchain(mp_chain);
+        return (NULL);
 }
 
 /* ARGSUSED */
 static void
 overlay_m_ioctl(void *arg, queue_t *q, mblk_t *mp)