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>

include/efi_selftest.h

@@ -60,6 +60,17 @@ void efi_st_exit_boot_services(void);
 void efi_st_printf(const char *fmt, ...)
 		 __attribute__ ((format (__printf__, 1, 2)));
 
+/*
+ * Compare memory.
+ * We cannot use lib/string.c due to different CFLAGS values.
+ *
+ * @buf1:	first buffer
+ * @buf2:	second buffer
+ * @length:	number of bytes to compare
+ * @return:	0 if both buffers contain the same bytes
+ */
+int efi_st_memcmp(const void *buf1, const void *buf2, size_t length);
+
 /*
  * Reads an Unicode character from the input device.
  *