Check for DMA mapping errors, recover from them and register them in
ethtool stats like other errors.

Cc: Rasesh Mody <rasesh.mody@qlogic.com>
Signed-off-by: NIvan Vecera <ivecera@redhat.com>
Acked-by: NRasesh Mody <rasesh.mody@qlogic.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>