enic: add stats for dma mapping error

This patch adds generic statistics for enic. As of now dma_map_error is the only
member. dma_map_erro is incremented every time dma maping error happens.

Signed-off-by: Govindarajulu Varadarajan <_govind@gmx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc drivers/net/ethernet/cisco/enic/enic.h
Simple merge

diff --cc drivers/net/ethernet/cisco/enic/enic_ethtool.c
Simple merge

diff --cc drivers/net/ethernet/cisco/enic/vnic_stats.h
Simple merge