iaxwifi200: disable background scans for now

It crashes the firmware after 40 scans. The issue has been reported to
OpenBSD, until then we can leave this disabled. The consequence is that
the wifi network list will not refresh while already connected to a
network. But at least the connection remains online.

src/add-ons/kernel/drivers/network/wlan/iaxwifi200/dev/pci/if_iwx.c

@@ -7423,6 +7423,11 @@ iwx_bgscan(struct ieee80211com *ic)
 	if (sc->sc_flags & IWX_FLAG_SCANNING)
 		return 0;
 
+#ifdef __HAIKU__
+	// Stops working after 40 scans and crashes the firmware, so let's not do it.
+	return EOPNOTSUPP;
+#endif
+
 	err = iwx_umac_scan_v14(sc, 1);
 	if (err) {
 		printf("%s: could not initiate scan\n", DEVNAME(sc));