base-files: support setting bridge MAC address

Fixes: 43fc720657 ("base-files: generate "device" UCI type section for bridge")
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>

package/base-files/files/bin/config_generate

@@ -114,10 +114,12 @@ generate_network() {
 			add network device
 			set network.@device[-1].name='br-$1'
 			set network.@device[-1].type='bridge'
+			set network.@device[-1].macaddr='$macaddr'
 		EOF
 		for port in $ports; do uci add_list network.@device[-1].ports="$port"; done
 		ifname=br-$1
 		type=
+		macaddr=""
 	}
 
 	[ -n "$bridge" ] && {