[ffwizard] fix macaddr for dhcp interface for wdr4900

there is an issue with the macaddr for wdr4900 (freifunk-berlin/firmware#122).
now if there is a macaddr set to lan interface we copy that to our dhcp
interface
Merge pull request #28 from freifunk-berlin/fix/macAddressForWDR4900

[ffwizard] fix macaddr for dhcp interface for wdr4900