gluon-mesh-batman-adv: add "gateway_tq" field to respondd statistics (#2596)

This new field reflects the TQ to the selected gateway.

Before this commit, if you had connectivity issues in a larger mesh,
it was a tedious task to understand which nodes are affected and which
are not. By providing this new value for each node, it becomes easier
to see which nodes are affected by the connectivity issues and which
are not.

The new field "gateway_tq" is located at the toplevel of the
statistics resource (next to "gateway" and "gateway_nexthop"):

    gluon-neighbour-info -d ::1 -r statistics
    {
        ...
        "gateway": "02:a1:71:04:09:10",
        "gateway_nexthop": "88:e6:40:20:90:10",
        "gateway_tq": 193,
        ...
    }

package/gluon-mesh-batman-adv/src/respondd-statistics.c

@@ -63,6 +63,7 @@ struct gw_netlink_opts {
 static const enum batadv_nl_attrs gateways_mandatory[] = {
 	BATADV_ATTR_ORIG_ADDRESS,
 	BATADV_ATTR_ROUTER,
+	BATADV_ATTR_TQ,
 };
 
 static int parse_gw_list_netlink_cb(struct nl_msg *msg, void *arg)
@@ -73,6 +74,7 @@ static int parse_gw_list_netlink_cb(struct nl_msg *msg, void *arg)
 	struct genlmsghdr *ghdr;
 	uint8_t *orig;
 	uint8_t *router;
+	uint8_t tq;
 	struct gw_netlink_opts *opts;
 	char addr[18];
 
@@ -100,11 +102,13 @@ static int parse_gw_list_netlink_cb(struct nl_msg *msg, void *arg)
 
 	orig = nla_data(attrs[BATADV_ATTR_ORIG_ADDRESS]);
 	router = nla_data(attrs[BATADV_ATTR_ROUTER]);
+	tq = nla_get_u8(attrs[BATADV_ATTR_TQ]);
 
 	sprintf(addr, "%02x:%02x:%02x:%02x:%02x:%02x",
 		orig[0], orig[1], orig[2], orig[3], orig[4], orig[5]);
 
 	json_object_object_add(opts->obj, "gateway", json_object_new_string(addr));
+	json_object_object_add(opts->obj, "gateway_tq", json_object_new_int(tq));
 
 	sprintf(addr, "%02x:%02x:%02x:%02x:%02x:%02x",
 		router[0], router[1], router[2], router[3], router[4], router[5]);