mlx5: support RETA query and update

mlx5: support RETA query and update

ConnectX-4 adapters do not have a constant indirection table size, which is
set at runtime from the number of RX queues. The maximum size is retrieved
using a hardware query and is normally 512.

Since the current RETA API cannot handle a variable size, any query/update
command causes it to be silently updated to RSS_INDIRECTION_TABLE_SIZE
entries regardless of the original size.

Also due to the underlying type of the configuration structure, the maximum
size is limited to RSS_INDIRECTION_TABLE_SIZE (currently 128, at most 256
entries).

A port stop/start must be done to apply the new RETA configuration.

Signed-off-by: Nelio Laranjeiro <nelio.laranjeiro@6wind.com>