gluon-mesh-batman-adv: increase bridge multicast querier robustness to 9

The RFC standard multicast querier interval is 120s. Our querier uses in
interval of 20s for better support of roaming clients, but our robustness
setting of 3 leads to external queriers using the standard interval to be
timeout after only 60s, leading to frequent "querier appeared/disappeared"
messages. Increase robustness so that external queriers with any interval
<180s are supported.

package/gluon-mesh-batman-adv/luasrc/lib/gluon/upgrade/320-gluon-mesh-batman-adv-client-bridge

@@ -18,7 +18,7 @@ uci:section('network', 'interface', 'client', {
 	peerdns = not site.dns.servers(),
 	sourcefilter = false,
 	keep_ra_dnslifetime = true,
-	robustness = 3,
+	robustness = 9,
 	query_interval = 2000,
 	query_response_interval = 500,
 })