netfilter: conntrack: Use flags in nf_ct_tmpl_alloc()

The flags were ignored for this function when it was introduced. Also
fix the style problem in kzalloc.

Fixes: 0838aa7f (netfilter: fix netns dependencies with conntrack
templates)
Signed-off-by: Joe Stringer <joestringer@nicira.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>