net: fastboot: Merge AOSP UDP fastboot

Merge UDP fastboot support from AOSP:

  https://android.googlesource.com/platform/external/u-boot/+/android-o-mr1-iot-preview-8

Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com>
Signed-off-by: Alex Deymo <deymo@google.com>
Signed-off-by: Jocelyn Bohr <bohr@google.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index 30cf63f..17ca0bb 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -655,8 +655,8 @@
 	  This enables the command "fastboot" which enables the Android
 	  fastboot mode for the platform. Fastboot is a protocol for
 	  downloading images, flashing and device control used on
-	  Android devices. Fastboot requires support for acting as a USB
-	  device.
+	  Android devices. Fastboot requires either the network stack
+	  enabled or support for acting as a USB device.
 
 	  See doc/README.android-fastboot for more information.