mlx4: add a new xmit_more counter

ethtool -S reports a new counter, tracking number of time doorbell
was not triggered, because skb->xmit_more was set.

$ ethtool -S eth0 | egrep "tx_packet|xmit_more"
     tx_packets: 2413288400
     xmit_more: 666121277

I merged the tso_packet false sharing avoidance in this patch as well.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc drivers/net/ethernet/mellanox/mlx4/en_ethtool.c
Simple merge

diff --cc drivers/net/ethernet/mellanox/mlx4/en_port.c
Simple merge

diff --cc drivers/net/ethernet/mellanox/mlx4/en_tx.c
Simple merge

diff --cc drivers/net/ethernet/mellanox/mlx4/mlx4_en.h
Simple merge