net/mlx5: introduce flow splitters chain

net/mlx5: introduce flow splitters chain

The mlx5 hardware has some limitations and flow might
require to be split into multiple internal subflows.
For example this is needed to provide the meter object
sharing between multiple flows or to provide metadata
register copying before final queue/rss action.

The multiple features might require several level of
splitting. For example, hairpin feature splits the
original flow into two ones - rx and tx parts. Then
RSS feature should split rx part into multiple subflows
with extended item sets. Then, metering feature might
require splitting each RSS subflow into meter jump
chain, and then metadata extensive support might
require the final subflows splitting. So, we have
to organize the chain of splitting subroutines to
abstract each level of splitting.

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