fff-gateway: make uci query for vlan ports quiet

The user might create a vlan without any ports.
This setup lead to "uci: Entry not found" error messages,
while still working as intended.

The '-q' flag is added to the corresponding uci query to
hide this error. While this isn't strictly necessary, the
uci subcommand is quoted to bring it in line with the other
subcommands.

Signed-off-by: Fabian Bläse <fabian@blaese.de>
Reviewed-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

src/packages/fff/fff-gateway/files/etc/gateway.d/20-vlan

@@ -10,7 +10,7 @@ BOARD="$(uci get board.model.name)"
 configure() {
 	add_vlan() {
 		local vlan="$1"
-		local ports=$(uci get gateway.$vlan.ports)
+		local ports="$(uci -q get gateway.$vlan.ports)"
 		local name="$SWITCHDEV"_$vlan
 
 		uci set network.$name='switch_vlan'