kvm tools: Use kernel dhcp for network autoconfiguration

kvm tools: Use kernel dhcp for network autoconfiguration

This patch removes the manual/usermode dhcp client configuration and instead
uses the DHCP client built within the kernel.

Since this client is tightly integrated with NFS (if NFS config is set), we
will add a specific NFS root addr in our DHCP offer to point it to a non
existent address so that we won't hang trying to poke it for our root.

Acked-by: Asias He <asias.hejun@gmail.com>
Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>