netifd: bridge: set default value for igmp_snoop

When unchecked the igmp snoop option for a bridge by luci, it
just delete the igmp_snooping key from the config file.
So netifd can't change /sys/devices/virtual/net/br-lan/bridge/multicast_snooping from "1" to "0".

Option multicast_querier seems no input entry in luci, but it's
an related option.

This patch will set a default value to false for the bridge
option to fix this bug.

Signed-off-by: Zheng Qian <sotux82@gmail.com>

bridge.c

@@ -877,6 +877,8 @@ bridge_apply_settings(struct bridge_state *bst, struct blob_attr **tb)
 	cfg->stp = false;
 	cfg->forward_delay = 2;
 	cfg->robustness = 2;
+	cfg->igmp_snoop = false;
+	cfg->multicast_querier = false;
 	cfg->query_interval = 12500;
 	cfg->query_response_interval = 1000;
 	cfg->last_member_interval = 100;