Jumbo frames support on ls1024a

[niggowai]

Hi,
it would be nice to have support for Jumbo Frames on the ls1024a. The stock kernel allows setting a mtu to 9000 (maybe even higher). However, the kernel here fails to set a mtu>1500. Using a higher mtu may reduce the load on the nas, since a nfs read is usually around 8k, what would fit in a 9k jumbo frame. With a 1500 mtu the nas would use 6 frames, so it also has to calculate 6 crc's instead of 1.

nas542:~# ip link set dev eth1 mtu 9000
[ 1268.740000] eth1: mtu greater than device maximum
ip: ioctl 0x8922 failed: Invalid argument