net/mlx5e: Count GSO packets correctly

TX packets statistics ('tx_packets' counter) used to count GSO packets
as one, even though it contains multiple segments.
This patch will increment the counter by the number of segments, and
align the driver with the behavior of other drivers in the stack.

Note that no information is lost in this patch due to 'tx_tso_packets'
counter existence.

Before, ethtool showed:
$ ethtool -S ens6 | egrep "tx_packets|tx_tso_packets"
     tx_packets: 61340
     tx_tso_packets: 60954
     tx_packets_phy: 2451115

Now, we will see the more logical statistics:
$ ethtool -S ens6 | egrep "tx_packets|tx_tso_packets"
     tx_packets: 2451115
     tx_tso_packets: 60954
     tx_packets_phy: 2451115

Fixes: e586b3b0 ("net/mlx5: Ethernet Datapath files")
Signed-off-by: Gal Pressman <galp@mellanox.com>
Cc: kernel-team@fb.com
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>