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>

lib/efi_selftest/efi_selftest_util.c

@@ -0,0 +1,25 @@
+/*
+ * efi_selftest_util
+ *
+ * Copyright (c) 2017 Heinrich Schuchardt <xypron.glpk@gmx.de>
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ *
+ * Utility functions
+ */
+
+#include <efi_selftest.h>
+
+int efi_st_memcmp(const void *buf1, const void *buf2, size_t length)
+{
+	const u8 *pos1 = buf1;
+	const u8 *pos2 = buf2;
+
+	for (; length; --length) {
+		if (*pos1 != *pos2)
+			return pos1 - pos2;
+		++pos1;
+		++pos2;
+	}
+	return EFI_ST_SUCCESS;
+}