net/mlx5: Introduce log_max_current_uc_list_wr_supported bit

Downstream patch will use this bit in order to know whether the device
supports changing of max_uc_list.

Signed-off-by: Shay Drory <shayd@nvidia.com>
Reviewed-by: Moshe Shemesh <moshe@nvidia.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>