treewide: remove "+" sign for increment with macaddr_add

Many people appear to use an unneeded "+" prefix for the increment
when calculating a MAC address with macaddr_add. Since this is not
required and used inconsistently [*], just remove it.

[*] As a funny side-fact, copy-pasting has led to almost all
    hotplug.d files using the "+", while nearly all of the
    02_network files are not using it.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/rockchip/armv8/base-files/etc/board.d/02_network

@@ -33,7 +33,7 @@ rockchip_setup_macs()
 	case "$board" in
 	friendlyarm,nanopi-r2s)
 		wan_mac=$(nanopi_r2s_generate_mac)
-		lan_mac=$(macaddr_add "$wan_mac" +1)
+		lan_mac=$(macaddr_add "$wan_mac" 1)
 		;;
 	esac