[TCP] tcp_probe: Attach printf attribute properly to printl().

GCC doesn't like the way Stephen initially did it:

net/ipv4/tcp_probe.c:83: warning: empty declaration
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp_probe.c

@@ -62,6 +62,9 @@ struct {
  * Print to log with timestamps.
  * FIXME: causes an extra copy
  */
+static void printl(const char *fmt, ...)
+	__attribute__ ((format (printf, 1, 2)));
+
 static void printl(const char *fmt, ...)
 {
 	va_list args;
@@ -80,8 +83,7 @@ static void printl(const char *fmt, ...)
 
 	kfifo_put(tcpw.fifo, tbuf, len);
 	wake_up(&tcpw.wait);
-} __attribute__ ((format (printf, 1, 2)));
-
+}
 
 /*
  * Hook inserted to be called before each receive packet.