efi_loader: stop network in EXIT_BOOT_SERVICES

efi_loader: stop network in EXIT_BOOT_SERVICES

It has been reported that memory corruption can occurred because network
packages where received after EXIT_BOOT_SERVICES. See the thread
starting at [1].

We try to remove all drivers when EXIT_BOOT_SERVICES is called. But

* Some network drivers don't call their own stop method when removed.
* Some network drivers don't have a remove method.
* Some devices have CONFIG_DM_DEVICE_REMOVE=n.

Let's call eth_halt() in EXIT_BOOT_SERVICES explicitly.

[1]
https://lore.kernel.org/all/C101B675-EEE6-44CB-8A44-83F72182FBD6@kohlschutter.com/

Cc: Michael Brown <mcb30@ipxe.org>
Reported-by: Christian Kohlschütter <christian@kohlschutter.com>
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Michael Brown <mcb30@ipxe.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Tested-by: Christian Kohlschütter <christian@kohlschutter.com>