headers_check fix: linux/if_ppp.h

fix the following 'make headers_check' warning:

  usr/include/linux/if_ppp.h:96: found __[us]{8,16,32,64} type without #include <linux/types.h>
Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>

include/linux/if_ppp.h

@@ -33,6 +33,7 @@
 #ifndef _IF_PPP_H_
 #define _IF_PPP_H_
 
+#include <linux/types.h>
 #include <linux/compiler.h>
 
 /*