Fix endianness bug introduced in r205091.

Fix endianness bug introduced in r205091.
After controller updates control word in a RX LE, driver converts
it to host byte order. The checksum value in the control word is
stored in big endian form by controller. r205091 didn't account for
the host byte order conversion such that the checksum value was
incorrectly interpreted on big endian architectures which in turn
made all TCP/UDP frames dropped. Make RX checksum offload work
on any architectures by swapping the checksum value.

Reported by:	Sreekanth M. ( kanthms <> netlogicmicro dot com )
Tested by:	Sreekanth M. ( kanthms <> netlogicmicro dot com )