Fix up detect-local-mode validation

Validate the --detect-local-mode value in the API object validation
rather than doing it separately later. Also, remove runtime checks and
unit tests for cases that would be blocked by validation

pkg/proxy/apis/config/validation/validation_test.go

@@ -424,6 +424,28 @@ func TestValidateKubeProxyConfiguration(t *testing.T) {
 			},
 			expectedErrs: field.ErrorList{field.Invalid(newPath.Child("InterfaceName"), "", "must not be empty")},
 		},
+		"invalid DetectLocalMode": {
+			config: kubeproxyconfig.KubeProxyConfiguration{
+				BindAddress:        "10.10.12.11",
+				HealthzBindAddress: "0.0.0.0:12345",
+				MetricsBindAddress: "127.0.0.1:10249",
+				ClusterCIDR:        "192.168.59.0/24",
+				ConfigSyncPeriod:   metav1.Duration{Duration: 1 * time.Second},
+				IPTables: kubeproxyconfig.KubeProxyIPTablesConfiguration{
+					MasqueradeAll: true,
+					SyncPeriod:    metav1.Duration{Duration: 5 * time.Second},
+					MinSyncPeriod: metav1.Duration{Duration: 2 * time.Second},
+				},
+				Conntrack: kubeproxyconfig.KubeProxyConntrackConfiguration{
+					MaxPerCore:            pointer.Int32(1),
+					Min:                   pointer.Int32(1),
+					TCPEstablishedTimeout: &metav1.Duration{Duration: 5 * time.Second},
+					TCPCloseWaitTimeout:   &metav1.Duration{Duration: 5 * time.Second},
+				},
+				DetectLocalMode: "Guess",
+			},
+			expectedErrs: field.ErrorList{field.NotSupported(newPath.Child("DetectLocalMode"), "Guess", []string{"ClusterCIDR", "NodeCIDR", "BridgeInterface", "InterfaceNamePrefix", ""})},
+		},
 	}
 
 	for name, testCase := range testCases {