node: dgram buffer size options and methods for Node 8.7.0 (#20535)

* dgram buffer size options and methods

* Verify type returned by dgram.*BufferSize methods

types/node/index.d.ts

@@ -2672,6 +2672,8 @@ declare module "dgram" {
     interface SocketOptions {
         type: SocketType;
         reuseAddr?: boolean;
+        recvBufferSize?: number;
+        sendBufferSize?: number;
     }
 
     export function createSocket(type: SocketType, callback?: (msg: Buffer, rinfo: RemoteInfo) => void): Socket;
@@ -2695,6 +2697,10 @@ declare module "dgram" {
         dropMembership(multicastAddress: string, multicastInterface?: string): void;
         ref(): this;
         unref(): this;
+        setRecvBufferSize(size: number): void;
+        setSendBufferSize(size: number): void;
+        getRecvBufferSize(): number;
+        getSendBufferSize(): number;
 
         /**
          * events.EventEmitter

types/node/node-tests.ts

@@ -1436,6 +1436,20 @@ namespace dgram_tests {
             let _rinfo: dgram.AddressInfo = rinfo;
         });
     }
+
+    {
+        let ds: dgram.Socket = dgram.createSocket({
+            type: 'udp4',
+            recvBufferSize: 10000,
+            sendBufferSize: 15000
+        });
+
+        let size: number;
+        size = ds.getRecvBufferSize();
+        ds.setRecvBufferSize(size);
+        size = ds.getSendBufferSize();
+        ds.setSendBufferSize(size);
+    }
 }
 
 ////////////////////////////////////////////////////