net/mlx5e: Avoid TX CQE generation if more xmit packets expected

In order to save PCI BW consumed by TX CQEs and to reduce the amount of
CPU cache misses caused by TX CQE reading, we request TX CQE generation
only when skb->xmit_more=0.

As a consequence of the above, a single TX CQE may now indicate the
transmission completion of multiple TX SKBs.

This also handles a problem introduced in commit b1b8105ebf41 "net/mlx5e:
Support NETIF_F_SG" where we didn't ask for NOP completions while the
driver didn't have the proper code to handle this case.

Fixes: b1b8105ebf41 ('net/mlx5e: Support NETIF_F_SG')
Signed-off-by: Achiad Shochat <achiad@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>