Don't hold a driver lock across bus_teardown_intr. Jhb points out

that one cannot generally hold a lock and call bus_teardown_intr.
This is race free with wi_intr because bus_teardown_intr won't allow
wi_intr to be called after it returns.

# jeff hsu points out that there might be a race between this unlock
# and wi_start.  While that may be true also, it won't impact this commit.

Submitted by: jhb

sys/dev/wi/if_wi.c

@@ -486,10 +486,9 @@ wi_detach(device_t dev)
 	ifmedia_removeall(&sc->sc_media);
 
 	ieee80211_ifdetach(ifp);
+	WI_UNLOCK(sc);
 	bus_teardown_intr(dev, sc->irq, sc->wi_intrhand);
 	wi_free(dev);
-
-	WI_UNLOCK(sc);
 #if __FreeBSD_version >= 500000
 	mtx_destroy(&sc->sc_mtx);
 #endif