iptables: add upstream patch fixing the message 'connlabel.conf not found'

In iptables versions 1.4.20 and 1.4.21, any call to iptables
would generate a message

    cannot open connlabel.conf, not registering 'connlabel' match: No
        such file or directory

This problem was reported at [1] and subsequently fixed with commit [2], but
no upstream release has been made since. This patch imports the fix into
Buildroot, awaiting a new release of iptables.

[1] http://marc.info/?l=netfilter-devel&m=140990442432002&w=2
[2] http://git.netfilter.org/iptables/commit/?id=825fbda5482a7d5ec5a6619c81fe07ff865c7d6e



Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>