hi, 

  for a network monitoring application I needed access to sk_buff's from
userspace. The current linux/skbuff.h headerfile cannot be included from
userspace applications due to various kernel .h vs. libc .h clashes. 

I basically pruned the #include statements by inserting #ifdef _KERNEL__
statements until gcc started complaining. Therefore nothing has changed in the
kernelspace implementation. But this minor change makes it possible to include
linux/skbuff.h from userspace. 

Ideally, all the #ifdef __KERNEL__ secured headerfile references should be
removed, since it is clear that skbuff.h doesn't really rely on them. Perhaps
some .c file does, but I didn't feel like finding out which one.

cheers,

  Willem