mlxsw: spectrum_buffers: Forbid changing multicast TCs' attributes

Commit e83c045e ("mlxsw: spectrum_buffers: Configure MC pool")
configured the threshold of the multicast TCs as infinite so that the
admission of multicast packets is only depended on per-switch priority
threshold.

Forbid the user from changing the thresholds of these multicast TCs and
their binding to a different pool.
Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Reviewed-by: Petr Machata <petrm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlxsw/spectrum_buffers.c

@@ -503,6 +503,8 @@ static int mlxsw_sp_sb_prs_init(struct mlxsw_sp *mlxsw_sp,
 		.min_buff = _min_buff,			\
 		.max_buff = _max_buff,			\
 		.pool_index = MLXSW_SP_SB_POOL_EGR_MC,	\
+		.freeze_pool = true,			\
+		.freeze_thresh = true,			\
 	}
 
 static const struct mlxsw_sp_sb_cm mlxsw_sp1_sb_cms_ingress[] = {