If IF_HANDOFF() or netisr_queue() fail, they will free the mbuf. When

this happens, set (m) to NULL or we'll try to free it a second time on
return.

Submitted by:	Pavel Gulchouck <gul@gul.kiev.ua>

sys/net/if_ppp.c

@@ -1579,6 +1579,7 @@ ppp_inproc(sc, m)
 	if (sc->sc_flags & SC_DEBUG)
 	    if_printf(ifp, "input queue full\n");
 	ifp->if_iqdrops++;
+	m = NULL;
 	goto bad;
     }
     ifp->if_ipackets++;