linuxmodule/FromHost: add ether handler

Previously, one would need to

	ifconfig dev down
	ifconfig dev hw ether 01:02:03:04:05:06
	ifconfig dev up

in order to change the MAC address of a FromDevice.  This commit adds a
handler that does all of this automatically, which means you can change the
MAC from a Script.

This is useful if you have a FromHost/ToHost that are hooked up to a
ToDevice/FromDevice and you want the MACs to match.  If the actual interface
might not actually be available at click initialization time, this handler
make it possible to adjust the FromHost once the FromDevice is attached.