mwan3: Use /128 for ipv6 if no other source address was found

Signed-off-by: Aaron Goodman <aaronjg@stanford.edu>

net/mwan3/files/usr/sbin/mwan3track

@@ -140,7 +140,8 @@ main() {
 						# https://bugs.openwrt.org/index.php?do=details&task_id=2897
 						# so get the IP address of the interface and use that instead
 						if echo $track_ip | grep -q ':'; then
-							ADDR=$(ip -6 addr ls dev "$DEVICE" | sed -ne '/\/128/d' -e 's/ *inet6 \([^ \/]*\).* scope global.*/\1/p')
+						        ADDR=$(ip -6 addr ls dev "$DEVICE" | sed -ne '/\/128/d' -e 's/ *inet6 \([^ \/]*\).* scope global.*/\1/p' | head -n1)
+							[ -z "$ADDR" ] && ADDR=$(ip -6 addr ls dev "$DEVICE" | sed -ne 's/ *inet6 \([^ \/]*\).* scope global.*/\1/p')
 							ping_protocol=6
 						fi
 						if [ $check_quality -eq 0 ]; then