net/mlx5e: CT, Fix multiple allocations and memleak of mod acts

In the Linux kernel, the following vulnerability has been resolved:

net/mlx5e: CT, Fix multiple allocations and memleak of mod acts

CT clear action offload adds additional mod hdr actions to the
flow's original mod actions in order to clear the registers which
hold ct_state.
When such flow also includes encap action, a neigh update event
can cause the driver to unoffload the flow and then reoffload it.

Each time this happens, the ct clear handling adds that same set
of mod hdr actions to reset ct_state until the max of mod hdr
actions is reached.

Also the driver never releases the allocated mod hdr actions and
causing a memleak.

Fix above two issues by moving CT clear mod acts allocation
into the parsing actions phase and only use it when offloading the rule.
The release of mod acts will be done in the normal flow_put().

backtrace:
[<000000007316e2f3>] krealloc+0x83/0xd0
[<00000000ef157de1>] mlx5e_mod_hdr_alloc+0x147/0x300 [mlx5_core]
[<00000000970ce4ae>] mlx5e_tc_match_to_reg_set_and_get_id+0xd7/0x240 [mlx5_core]
[<0000000067c5fa17>] mlx5e_tc_match_to_reg_set+0xa/0x20 [mlx5_core]
[<00000000d032eb98>] mlx5_tc_ct_entry_set_registers.isra.0+0x36/0xc0 [mlx5_core]
[<00000000fd23b869>] mlx5_tc_ct_flow_offload+0x272/0x1f10 [mlx5_core]
[<000000004fc24acc>] mlx5e_tc_offload_fdb_rules.part.0+0x150/0x620 [mlx5_core]
[<00000000dc741c17>] mlx5e_tc_encap_flows_add+0x489/0x690 [mlx5_core]
[<00000000e92e49d7>] mlx5e_rep_update_flows+0x6e4/0x9b0 [mlx5_core]
[<00000000f60f5602>] mlx5e_rep_neigh_update+0x39a/0x5d0 [mlx5_core]