[qmp-system]: reset wifi when configured and operating channels differ

This script checks that, for every wireless device configured by qMp (in
/etc/config/qmp), the channel configured in /etc/config/wireless and the one
reported by the "iw" command match. If they differ, it resets the wifi system.

First part of #470
Signed-off-by: Roger Pueyo Centelles <roger.pueyo@guifi.net>

packages/qmp-system/files/usr/bin/wifihealth.sh

+#!/bin/sh
+
+# This script checks if the wireless devices configured in /etc/config/qmp are
+# operating in the channel they are configured to. It is useful to go back to
+# the configured channel if DFS switches the device to another one.
+
+# Make sure there is at least one wireless device configured
+lastdev=$(uci -q get qmp.@wireless[-1].device)
+if [ $lastdev ]; then
+
+	# Iterate through all the configured devices
+	i=0
+	while [ $i -ge 0 ]; do
+
+		# Get qMp device configuration parameters
+		qmpdev=$(uci -q get qmp.@wireless[${i}].device)
+		qmpmode=$(uci -q get qmp.@wireless[${i}].mode)
+		qmpchannel=$(uci -q get qmp.@wireless[${i}].channel)
+
+		# Check the device is not disabled in qMp, skip it otherwise
+		if [ "$qmpmode" != "none" ]; then
+
+			wifiradio=$(uci -q get wireless.$qmpdev.device)
+			if [ $wifiradio ]; then
+
+				wifichannel=$(uci get wireless.${wifiradio}.channel)
+
+				if [ $wifichannel ]; then
+					iwchannel=$(iw dev $qmpdev info | grep channel | sed -e 's/^[ \t]*//' | cut -d ' ' -f 2)
+
+					# Trim the HT40 upper/lower channel extension info (i.e., the + or - symbols)
+					qmpchannelnum=$(echo ${qmpchannel} | sed -e 's/[-+]*//g')
+					wifichannelnum=$(echo ${wifichannel} | sed -e 's/[-+]*//g')
+
+					# Check that channel configurations in /etc/config/qmp and /etc/config/wireless match
+					if [ "$qmpchannelnum" == "$wifichannelnum" ]; then
+
+						# If the channel configured in /etc/config/wireless and the one reported by iw differ, reset the wifi
+						if [ $wifichannelnum -ne $iwchannel ]; then
+							wifi
+							exit 0
+						fi
+					fi
+				fi
+			fi
+
+		fi
+
+		if [ "$(uci -q get qmp.@wireless[${i}].device)" == "$(uci -q get qmp.@wireless[-1].device)" ]; then
+			i=-1
+		else
+			let i=$i+1
+		fi
+	done
+fi