[GSoC] Making vkernels checkpointable - week4

Hello,

This week I was working on restoring network interface after thawing a
vkernel from a checkpoint. What I have to do was to reopen appropriate
device file, bring it up then either set TAP address or tie it to a
bridge. In order to be able to do all this I had to store some
information originally discarded once network interfaces are set up.
Mainly TAP device fle name and either TAP address or bridge file name
were needed. Finally, vke_softc structure had to be updated with new
TAP device file descriptor and TAP device unit.

Paweł