wprobe: fix compile error because of missing isnan()

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@17468 3c298f89-4303-0410-b956-a3cf2f4a3e73

package/wprobe/src/user/wprobe-lib.c

@@ -13,6 +13,8 @@
  * GNU General Public License for more details.
  */
 
+#define _ISOC99_SOURCE
+#define _BSD_SOURCE
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <stdio.h>