gluon-client-bridge: set ra_holdoff interval to 30 seconds (#1597)

Allow odhcp6c to fork the script to handle router
advertisments in 30 seconds intervals. This is the value
that was previously used in Gluon v2018.1 / LEDE 17.01.

The default value is 3 seconds and while it is RFC compliant
it can put alot of pressure on even moderately sized devices.

Signed-off-by: Martin Weinelt <martin@darmstadt.freifunk.net>

package/gluon-client-bridge/luasrc/lib/gluon/upgrade/300-gluon-client-bridge-network

@@ -35,6 +35,7 @@ uci:section('network', 'interface', 'client', {
 	macaddr = sysconfig.primary_mac,
 	igmp_snooping = true,
 	multicast_querier = true,
+	ra_holdoff = 30,
 })
 
 uci:save('network')