[libvirt] [RFC PATCH] Set and reset MAC for PASSTHROUGH mode

there is a problem present in libvirt that when a PASSTHROUGH mode DIRECT NIC connection is made the MAC address of the NIC is not automatically set and reset to the configured VM MAC and back again. The attached patch fixes this problem by setting and resetting the MAC while remembering the previous setting while the VM is running. This also works if libvirtd is restarted while the VM is running. The storing of the previous MAC address is done in a link ( currently in /tmp, but should probably go into /var/run somewhere ). Best regards Dirk