sandbox: eth: Add a bridge to a real network for sandbox

Implement a bridge between U-Boot's network stack and Linux's raw packet
API allowing the sandbox to send and receive packets using the host
machine's network interface.

This raw Ethernet API requires elevated privileges.  You can either run
as root, or you can add the capability needed like so:

sudo /sbin/setcap "CAP_NET_RAW+ep" /path/to/u-boot

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/net/Kconfig b/drivers/net/Kconfig
index e46e57b..5bd66ea 100644
--- a/drivers/net/Kconfig
+++ b/drivers/net/Kconfig
@@ -29,4 +29,14 @@
 
 	  This driver is particularly useful in the test/dm/eth.c tests
 
+config ETH_SANDBOX_RAW
+	depends on DM_ETH && SANDBOX
+	default y
+	bool "Sandbox: Bridge to Linux Raw Sockets"
+	help
+	  This driver is a bridge from the bottom of the network stack
+	  in U-Boot to the RAW AF_PACKET API in Linux. This allows real
+	  network traffic to be tested from within sandbox. See
+	  board/sandbox/README.sandbox for more details.
+
 endif # NETDEVICES