net: sandbox: Allow fake eth to handle more than 1 packet response

Use up to the max allocated receive buffers so as to be able to test
more complex situations.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
2 files changed