NET: pktgen - fix compile warning

This should fix the following warning:

net/core/pktgen.c: In function ‘pktgen_if_write’:
net/core/pktgen.c:890: warning: comparison of distinct pointer types lacks a cast
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
Reviewed-by: Nelson Elhage <nelhage@ksplice.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/core/pktgen.c

@@ -887,7 +887,7 @@ static ssize_t pktgen_if_write(struct file *file,
 	i += len;
 
 	if (debug) {
-		size_t copy = min(count, 1023);
+		size_t copy = min_t(size_t, count, 1023);
 		char tb[copy + 1];
 		if (copy_from_user(tb, user_buffer, copy))
 			return -EFAULT;