net/mlx5: fix dirty array of actions

net/mlx5: fix dirty array of actions

Previous patch changed the format of struct
mlx5_flow_dv_modify_hdr_resource, to use a flexible array for
modification actions.
In __flow_dv_translate() a union was defined with item of this struct,
and an array of maximal possible size.
Array elements are filled in several functions.
In function flow_dv_convert_action_set_reg(), array element is filled
partially, while the other fields of this array element are left
uninitialized.
This may cause failure of flow_dv_modify_hdr_resource_register()
when calling driver function with the 'dirty' array.

This patch updates flow_dv_convert_action_set_reg(), setting the
selected array element fields while clearing the other fields.
Other functions that fill the same array elements are also updated
for clarity and proofing future use.

Fixes: 024e95759c16 ("net/mlx5: fix modify actions support limitation")
Cc: stable@dpdk.org
Signed-off-by: Dekel Peled <dekelp@mellanox.com>
Acked-by: Matan Azrad <matan@mellanox.com>
Acked-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>