silence iwm dmesg spam from unhandled firmware responses

[Stefan Sperling]

Some iwm devices still produce a lot of "unhandled firmware reponse"
messages. These are only meaningful for debugging purposes, so silence
them unless debug mode is enabled.

Of course, users will still see the symptoms of any problems which
arise from unhandled firmware responses. This is just a cosmetic change.

Index: if_iwm.c
===================================================================
RCS file: /cvs/src/sys/dev/pci/if_iwm.c,v
retrieving revision 1.228
diff -u -p -r1.228 if_iwm.c
--- if_iwm.c    28 Apr 2018 16:05:56 -0000      1.228
+++ if_iwm.c    14 May 2018 12:39:37 -0000
@@ -7077,6 +7077,7 @@ do {                                                      
                \
 void
 iwm_notif_intr(struct iwm_softc *sc)
 {
+       struct ifnet *ifp = IC2IFP(&sc->sc_ic);
        uint16_t hw;
 
        bus_dmamap_sync(sc->sc_dmat, sc->rxq.stat_dma.map,
@@ -7339,10 +7340,11 @@ iwm_notif_intr(struct iwm_softc *sc)
                }
 
                default:
-                       printf("%s: unhandled firmware response 0x%x/0x%x "
-                           "rx ring %d[%d]\n",
-                           DEVNAME(sc), pkt->hdr.code, pkt->len_n_flags, qid,
-                           idx);
+                       if (ifp->if_flags & IFF_DEBUG)
+                               printf("%s: unhandled firmware response "
+                                   "0x%x/0x%x rx ring %d[%d]\n",
+                                   DEVNAME(sc), pkt->hdr.code,
+                                   pkt->len_n_flags, qid, idx);
                        break;
                }