net: asix: don't pad odd-length TX packets

net: asix: don't pad odd-length TX packets

For Ethernet/USB RX packets, the ASIX HW pads odd-sized packets so that
they have an even size. Currently, asix_recv() does remove this padding,
and asic_send() adds equivalent padding in the TX path. However, the HW
does not appear to need this packing for TX packets in practical testing
with "ASIX Elec. Corp. AX88x72A 000001" Vendor: 0x0b95 Product 0x7720
Version 0.1. The Linux kernel does no such padding for the TX path.

Remove the padding from the TX path:

* For consistency with the Linux kernel.
* NVIDIA has a Tegra simulator which validates that the length of USB
  packets sent to an ASIX device matches the packet length value inside
  the packet data. Having U-Boot and the kernel do the same thing when
  creating the TX packets simplifies the simulator's validation.

Cc: Lucas Stach <dev@lynxeye.de>
Cc: Marek Vasut <marex@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Simon Glass <sjg@chromium.org>
Acked-by: Marek Vasut <marex@denx.de>
Tested-by: Marek Vasut <marex@denx.de>
Tested-by: Gerhard Sittig <gsi@denx.de>