net/mlx5: add no-inline Tx flag

net/mlx5: add no-inline Tx flag

This patch adds support for dynamic flag that hints transmit
datapath do not copy data to the descriptors. This flag is
useful when data are located in the memory of another (not NIC)
physical device and copying to the host memory is undesirable.

This hint flag is per mbuf for multi-segment packets.

This hint flag might be partially ignored if:

- hardware requires minimal data header to be inline into
  descriptor, it depends on the hardware type and its configuration.
  In this case PMD copies the minimal required number of bytes to
  the descriptor, ignoring the no inline hint flag, the rest of data
  is not copied.

- VLAN tag insertion offload is requested and hardware does not
  support this options. In this case the VLAN tag is inserted by
  software means and at least 18B are copied to descriptor.

Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
Acked-by: Matan Azrad <matan@mellanox.com>