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>