Remove support for macvtap devices

We don't have any use for them.
Split port hooks in to (create|remove|up|down) actions

The port hooks formerly had two functions that brought the device
up or down. That caused some problems with hotplugging of the zones.

Now the entire process has been split into four functions that
every port hooks has to implement.

create:
	Creates the device but does not bring it up yet. This will
	usually trigger a hotplug event so that various other port
	or zone hooks can attach the device or do similar actions.

up:
	Essentially brings up the device, just like:
	  ip link set devX up

	The action should propagate to any slave devices.

down:
	Does essentially the opposite of "up" and should propagate
	to the slaves as well.

remove:
	Removes any virtual devices and cleans up. This will also
	trigger a hotplug event so that all connected hooks will
	be notified about the removal.