mlxsw: spectrum: Veto sampling if already enabled on port

The per-port sampling triggers (i.e., ingress / egress) cannot be
enabled twice. Meaning, the below configuration will not result in
packets being sampled twice:

 # tc filter add dev swp1 ingress matchall skip_sw action sample rate 100 group 1
 # tc filter add dev swp1 ingress matchall skip_sw action sample rate 100 group 1

Therefore, reject such configurations.

Fixes: 90f53c53 ("mlxsw: spectrum: Start using sampling triggers hash table")
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

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

@@ -2668,6 +2668,11 @@ mlxsw_sp_sample_trigger_params_set(struct mlxsw_sp *mlxsw_sp,
 		return mlxsw_sp_sample_trigger_node_init(mlxsw_sp, &key,
 							 params);
 
+	if (trigger_node->trigger.local_port) {
+		NL_SET_ERR_MSG_MOD(extack, "Sampling already enabled on port");
+		return -EINVAL;
+	}
+
 	if (trigger_node->params.psample_group != params->psample_group ||
 	    trigger_node->params.truncate != params->truncate ||
 	    trigger_node->params.rate != params->rate ||