net/mlx5: configure Rx queue for buffer split

net/mlx5: configure Rx queue for buffer split

The scatter-gather elements should be configured
accordingly to support the buffer split feature.
The application provides the desired settings for
the segments at the beginning of the packets and
PMD pads the buffer chain (if needed) with attributes
of last specified segment to accommodate the packet
of maximal length.

There are some limitations are implied. The MPRQ
feature should be disengaged if split is requested,
due to MPRQ neither supports pushing data to the
dedicated pools nor follows the flexible buffer sizes.
The vectorized rx_burst routines does not support
the scattering (these ones are extremely simplified
and work over the single segment only) and can't
handle split as well.

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