Issue 1498 - Look for iptables on the system first

Issue 1498 - Look for iptables on the system first

Lollipop needs iptables as PIE executable, the one we ship doesn't fit the bill.

Fortunately, Android has been shipping an iptables executable we can use since around Honeycomb - so with this patch we're looking for iptables on the system first.

(Note that there's another patch for this against adblockplusandroid 1.2.1, with some discussion: http://codereview.adblockplus.org/6006698351263744/)

[Felix Dahlke, 2015-01-14 18:31:13]

Note that we can most likely increase the minSdkVersion to Honeycomb and just
get rid of the iptables binary we ship altogether. However, I'd like to tackle
that separately, and land this fix for now.

[Wladimir Palant, 2015-01-14 18:42:29]

LGTM