add a function to set the UDP send buffer size

This function is the equivalent to the function used to set the UDP
receive buffer size. It's so similar that code generation is used to
make a copy of the setReceiveBuffer function.

sys_conn_oob.go

@@ -42,6 +42,17 @@ func inspectReadBuffer(c syscall.RawConn) (int, error) {
 	return size, serr
 }
 
+func inspectWriteBuffer(c syscall.RawConn) (int, error) {
+	var size int
+	var serr error
+	if err := c.Control(func(fd uintptr) {
+		size, serr = unix.GetsockoptInt(int(fd), unix.SOL_SOCKET, unix.SO_SNDBUF)
+	}); err != nil {
+		return 0, err
+	}
+	return size, serr
+}
+
 type oobConn struct {
 	OOBCapablePacketConn
 	batchConn batchConn