[U-Boot] dm9000 patch tftp, nfs fixes.

Hi,

I start a project on a freescale imx27 using the dm9000a for network.

I learned that the tftp , nfs and other network related working more less very unstable. I start compare the dm9000.c code with the upstream kernel v3.8.4 and fix some issues.

issues tftp with many bad checksums and timeouts nfs with not working at all when upload a 38Mbyte rootfs.jffs2

After the patch its works much better for me. please find my patch attached and consider to merge it the the head branch.

cheers Chris