net/mlx5e: HTB, reduce visibility of htb functions

No need to expose all htb tc functions to the main driver file,
expose only the master htb tc function mlx5e_htb_setup_tc()
which selects the internal "now static" function to call.

Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Moshe Tal <moshet@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Reviewed-by: Maxim Mikityanskiy <maximmi@nvidia.com>