log/syslog: return length of data provided by the user, not length of header

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/5644059

src/pkg/log/syslog/syslog.go

@@ -136,11 +136,19 @@ func (w *Writer) Debug(m string) (err error) {
 }
 
 func (n netConn) writeBytes(p Priority, prefix string, b []byte) (int, error) {
-	return fmt.Fprintf(n.conn, "<%d>%s: %s\n", p, prefix, b)
+	_, err := fmt.Fprintf(n.conn, "<%d>%s: %s\n", p, prefix, b)
+	if err != nil {
+		return 0, err
+	}
+	return len(b), nil
 }
 
 func (n netConn) writeString(p Priority, prefix string, s string) (int, error) {
-	return fmt.Fprintf(n.conn, "<%d>%s: %s\n", p, prefix, s)
+	_, err := fmt.Fprintf(n.conn, "<%d>%s: %s\n", p, prefix, s)
+	if err != nil {
+		return 0, err
+	}
+	return len(s), nil
 }
 
 func (n netConn) close() error {