e1000: fix endianness issues

e1000: fix endianness issues

This patch fixes endianness issues in the e1000 nic emulation, which
currently only works on little endian hosts with little endian targets.

Byte swapping does not depend on host endianness, so this patch remove
the use of cpu_to_le32 and le32_to_cpu functions. It depends on the path
from the CPU to the device, which is currently and *wrongly* implemented
in Qemu as a byteswap on big endian targets. This patch does the same
as in other devices emulation as all the currently implemented targets
work with this implementation.

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@4046 c046a42c-6fe2-441c-8c8c-71466251a162