net/mlx5e: CT, Don't set flow flag CT for ct clear flow

ct clear action is a normal flow with a modify header for registers to
0. there is no need for any special handling in tc_ct.c.
Parsing of ct clear action still allocates mod acts to set 0 on the
registers and the driver continue to add a normal rule with modify hdr
context.

Signed-off-by: Roi Dayan <roid@nvidia.com>
Reviewed-by: Oz Shlomo <ozsh@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>