efi_loader: supply EFI network test

efi_loader: supply EFI network test

This patch provides an EFI application to check the correct function
of the Simple Network Protocol implementation.

It sends a DHCP request and analyzes the DHCP offer.

Different error conditions including a 10s timeout are checked.

A successful execution will look like this:

=> bootefi nettest
Scanning disk ide.blk#0...
Found 1 disks
WARNING: Invalid device tree, expect boot to fail
Network test
DHCP Discover
DHCP reply received from 192.168.76.2 (52:55:c0:a8:4c:02)
as broadcast message.
OK. The test was completed successfully.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Alexander Graf <agraf@suse.de>