net/mlx5e: Tx, Soften inline mode VLAN dependencies

If capable, use zero inline mode in TX WQE for non-VLAN packets.
For VLAN ones, keep the enforcement of at least L2 inline mode,
unless the WQE VLAN insertion offload cap is on.

Performance:
Tested single core packet rate of 64Bytes.

NIC: ConnectX-5
CPU: Intel(R) Xeon(R) Gold 6154 CPU @ 3.00GHz

pktgen:
Before: 12.46 Mpps
After:  14.65 Mpps (+17.5%)

XDP_TX:
The MPWQE flow is not affected, as it already has this optimization.
So we test with priv-flag xdp_tx_mpwqe: off.

Before:  9.90 Mpps
After:  10.20 Mpps (+3%)

Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
Tested-by: Noam Stolero <noams@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>