Fix mtu requirement bug

There a bug with the MTU field in terraform where ExactlyOneOf
requires Jumbo or MTU to be set, but the intent was to allow
at most one of those fields to be set, but are optional.

ibm/service/power/resource_ibm_pi_network.go

@@ -75,19 +75,19 @@ func ResourceIBMPINetwork() *schema.Resource {
 				Description: "PI network gateway",
 			},
 			helpers.PINetworkJumbo: {
-				Type:         schema.TypeBool,
-				Optional:     true,
-				Computed:     true,
-				Deprecated:   "deprecated use pi_network_mtu instead",
-				ExactlyOneOf: []string{helpers.PINetworkMtu, helpers.PINetworkJumbo},
-				Description:  "PI network enable MTU Jumbo option",
+				Type:          schema.TypeBool,
+				Optional:      true,
+				Computed:      true,
+				Deprecated:    "deprecated use pi_network_mtu instead",
+				ConflictsWith: []string{helpers.PINetworkMtu},
+				Description:   "PI network enable MTU Jumbo option",
 			},
 			helpers.PINetworkMtu: {
-				Type:         schema.TypeInt,
-				Optional:     true,
-				Computed:     true,
-				ExactlyOneOf: []string{helpers.PINetworkMtu, helpers.PINetworkJumbo},
-				Description:  "PI Maximum Transmission Unit",
+				Type:          schema.TypeInt,
+				Optional:      true,
+				Computed:      true,
+				ConflictsWith: []string{helpers.PINetworkJumbo},
+				Description:   "PI Maximum Transmission Unit",
 			},
 			helpers.PINetworkAccessConfig: {
 				Type:         schema.TypeString,