r8169 2.4.32 backport of change mtu

Kernel 2.4.32 r8169 driver was missing change MTU.
It is back-ported from the kernel 2.6.16 r8169 driver. Performance went from 40 megabyte/second (MTU 1500) to 58 megabyte/second (MTU 7200) when testing with custom http server and wget for client. Target and destination were both tmpfs volumes.

Feedback requested: Did I do it right? Does it work for you?