efi: Use device device path type Messaging for network interface node

When adding network interface node use Messaging device path with
subtype MAC Address and device's MAC address as a value instead
of Media Device path type with subtype File Path and path "Net"

Signed-off-by: Oleksandr Tymoshenko <gonzo@bluezbox.com>
Signed-off-by: Alexander Graf <agraf@suse.de>