dma_rmb() barrier is added to load the long term buffer before copying
it to socket buffer; and dma_wmb() barrier is added to update the
long term buffer before it being accessed by VIOS (virtual i/o server).

Fixes: 032c5e82 ("Driver for IBM System i/p VNIC protocol")
Signed-off-by: NLijun Pan <ljp@linux.ibm.com>
Acked-by: NThomas Falcon <tlfalcon@linux.ibm.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>