Add support for Linksys EA6350 v3

I first want to thank @NoTengoBattery and all the other contributors on this effort. Much of what was contributed for support of current Linksys devices has been and will be very valuable in

One thing that I noticed in that work is that the extraction of the MAC address from the devinfo partition seems to be not quite right, as macaddr_add expects a string for its first argument, not a sh-executed result from that string. On the EA8300, there is an error that posts to the console, but not to the logs about this. I don't have an EA6350 V3 on hand so I can't test it, but I believe that the following patch should correct this issue

--- a/target/linux/ipq40xx/base-files/etc/board.d/02_network
+++ b/target/linux/ipq40xx/base-files/etc/board.d/02_network
@@ -64,7 +64,7 @@ ipq40xx_setup_macs()
                ;;
        linksys,ea6350v3)
                wan_mac=$(mtd_get_mac_ascii devinfo hw_mac_addr)
-               lan_mac=$(macaddr_add $(wan_mac) +1)
+               lan_mac=$(macaddr_add ${wan_mac} 1)
                ;;
        esac

Reference /lib/functions/system.sh

macaddr_add() {
        local mac=$1
        local val=$2
        local oui=${mac%:*:*:*}
        local nic=${mac#*:*:*:}

        nic=$(printf "%06x" $((0x${nic//:/} + $val & 0xffffff)) | sed 's/^\(.\{2\}\)\(.\{2\}\)\(.\{2\}\)/\1:\2:\3/')
        echo $oui:$nic
}
root@OpenWrt:~# wan_mac=11:22:33:44:55:66
root@OpenWrt:~# echo ${wan_mac}
11:22:33:44:55:66
root@OpenWrt:~# echo $(wan_mac)
-ash: wan_mac: not found