net/mlx5e: Introduce root ft concept for representors netdevs

Uplink representor traffic will be redirected to an empty root ft rather
than directly to a direct tir or ttc table, this root ft will be empty and
will be used as a link for auto-chaining with ttc table or ethtool tables
in downstream patches.

On load, fs core will connect uplink rep root_ft with ttc table.  In case
ethtool steering will be used, fs core will auto connect root_ft with
the ethtool bypass tables, which will be connected with the ttc table.

vport_rx_rule[uplink_rep]->root_ft->ethtool->ttc.

For non-uplink representors, for simplicity root_ft will always point at
ttc table, hence the replace vport_rx rule logic is removed.

vport_rx_rule[non_uplink_rep]->root_ft(ttc).

For now ethtool steering support can only be available on uplink rep.

Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>