Why I can't compile a simple netfilter hook module?

[Jonathan Neuschäfer]

On Tue, May 08, 2012 at 01:07:43AM -0300, Chir0n wrote:
> /home/fabio/Desktop/modules/hello.c:19:18: error: ‘NF_IP_PRE_ROUTING’
> undeclared (first use in this function)

This symbol is declared in a section that's "only for userspace
compatibility" (netfilter_ipv4.h, line 10).

HTH,
	Jonathan Neuschäfer