netfilter: nf_tables: fix implicit include of module.h

This file clearly uses modular infrastructure but does not call
out the inclusion of <linux/module.h> explicitly.  We add that
include explicitly here, so we can tidy up some header usage
elsewhere w/o causing build breakage.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>