Fix (I think!) the scan timeouts on the intel NICs.

This field needs to be (a) set, and (b) greater than the other timeouts
(passive, active, maxquiet, etc.)  It also is in microseconds, not
milliseconds.

I hope this will fix the scan hangs that people are seeing.

Obtained from:	Linux iwlwifi

sys/dev/iwn/if_iwn.c

@@ -6184,6 +6184,11 @@ iwn_scan(struct iwn_softc *sc)
 	 */
 	hdr->quiet_time = htole16(10);		/* timeout in milliseconds */
 	hdr->quiet_threshold = htole16(1);	/* min # of packets */
+	/*
+	 * Max needs to be greater than active and passive and quiet!
+	 * It's also in microseconds!
+	 */
+	hdr->max_svc = htole32(250 * 1000);
 
 	/* Select antennas for scanning. */
 	rxchain =