net/mlx5: DR, Fix wrong action data allocation in decap action

When TUNNEL_L3_TO_L2 decap action was created, a pointer to a local
variable was passed as its HW action data, resulting in attempt to
free invalid address:

  BUG: KASAN: invalid-free in mlx5dr_action_destroy+0x318/0x410 [mlx5_core]

Fixes: 4781df92

 ("net/mlx5: DR, Move STEv0 modify header logic")
Signed-off-by: Yevgeny Kliteynik <kliteyn@nvidia.com>
Reviewed-by: Alex Vesker <valex@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>