kernel: fix compile error in 3.12

Upstream commit c655bc6896b94ee0223393f26155c6daf1e2d148 changed number of
arguments in nf_ct_iterate_cleanup() function.

Signed-off-by: Luka Perkov <luka@openwrt.org>

SVN-Revision: 38547

target/linux/generic/patches-3.12/604-netfilter_conntrack_flush.patch

@@ -22,7 +22,7 @@
 +			return -EFAULT;
 +
 +		if (c == 'f')
-+			nf_ct_iterate_cleanup(net, kill_all, NULL);
++			nf_ct_iterate_cleanup(net, kill_all, NULL, 0, 0);
 +	}
 +	return count;
 +}