headers_check fix: linux/ppp_defs.h

fix the following 'make headers_check' warning:

  usr/include/linux/ppp_defs.h:50: found __[us]{8,16,32,64} type without #include <linux/types.h>
Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>

include/linux/ppp_defs.h

@@ -25,6 +25,8 @@
  * OR MODIFICATIONS.
  */
 
+#include <linux/types.h>
+
 /*
  *  ==FILEVERSION 20000114==
  *