Don't set xtables_{matches,targets} to NULL.

[chruss2]

Protocol-independent extensions will be looked up once for each protocol
and added to the protocol-specific cache.

Fixes #282.

[coveralls]

Coverage decreased (-0.05%) to 58.507% when pulling 282c790 on chruss2:master into 7fe9a99 on ldx:master.

[ldx]

Interesting, do you have some example code that can reproduce the original issue in #282?

[chruss2]

Sure. It requires a fairly recent libxtables, so alpine 3.10 is an easy way to reproduce it. Here is a docker one-liner.

docker run --privileged alpine:3.10 sh -c 'apk add python3-dev alpine-sdk iptables ip6tables; pip3 install python-iptables; XTABLES_LIBDIR=/usr/lib/xtables python3 -c "import sys; import iptc; match = iptc.Match(iptc.Rule(), \"addrtype\"); match6 = iptc.Match(iptc.Rule6(), \"addrtype\")"'

[ldx]

Looks good, thanks! 👍

[a-martynovich]

This patch leads to a freeze with 100% CPU usage with iptables older than 1.8.0. Try it on Ubuntu 18.04 for instance.
This patch needs to be applied only if iptables is 1.8.0 or newer.

[ldx]

I have 1.6.0 and not seeing this problem, any chance you can provide some example code that reproduces the issue?