efi_loader: Revert device_handle to disk after net boot

When you boot an efi payload from network, then exit that payload
and load another payload from disk afterwords, the disk payload will
currently see the network device as its boot path.

This breaks grub2 for example which tries to find its modules based
on the path it was loaded from.

This patch fixes that issue by always reverting to disk paths if we're
not in the network boot. That way the data structures after a network
boot look the same as before.

Signed-off-by: Alexander Graf <agraf@suse.de>