feature: Decrease WIFI Beacon rate in Mesh mode to around 2 times a second.

This changes the beacon rate from once every 100tu's to once every 500tu's

1tu=1024 microseconds

This will decrease the amount of RF time being used by beacon packets.

This is especially important on 900MHz and 2.4GHz using 5MHz wide channels where 10 nodes beaconing 10x a second at ~256kbit/s can use up around 45% of the RF channel in beacons alone.
Other bands and channels and widths are not expected to see as significant an advantage due to the faster data rates.

files/etc/config.mesh/wireless

@@ -5,6 +5,7 @@ config wifi-device  radio0
         option distance <wifi_distance>
         option country <wifi_country>
 	option htmode	HT20
+	option beacon_int 500
 include /etc/aredn_include/radio0path
 
 config wifi-iface