Revert vendor directory to support old golang (GOPATH mode)

gomodule is still in progress to migrate for now, hence multus
team decide to keep vendor directory to support build without
gomodule.

vendor/google.golang.org/grpc/codec.go

@@ -0,0 +1,50 @@
+/*
+ *
+ * Copyright 2014 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+import (
+	"google.golang.org/grpc/encoding"
+	_ "google.golang.org/grpc/encoding/proto" // to register the Codec for "proto"
+)
+
+// baseCodec contains the functionality of both Codec and encoding.Codec, but
+// omits the name/string, which vary between the two and are not needed for
+// anything besides the registry in the encoding package.
+type baseCodec interface {
+	Marshal(v interface{}) ([]byte, error)
+	Unmarshal(data []byte, v interface{}) error
+}
+
+var _ baseCodec = Codec(nil)
+var _ baseCodec = encoding.Codec(nil)
+
+// Codec defines the interface gRPC uses to encode and decode messages.
+// Note that implementations of this interface must be thread safe;
+// a Codec's methods can be called from concurrent goroutines.
+//
+// Deprecated: use encoding.Codec instead.
+type Codec interface {
+	// Marshal returns the wire format of v.
+	Marshal(v interface{}) ([]byte, error)
+	// Unmarshal parses the wire format into v.
+	Unmarshal(data []byte, v interface{}) error
+	// String returns the name of the Codec implementation.  This is unused by
+	// gRPC.
+	String() string
+}