Set ip_conntrack_tcp_be_liberal to improve network stability

[StefanScherer]

Add echo 1 > /proc/sys/net/ipv4/netfilter/ip_conntrack_tcp_be_liberal into build.

Fixes #57

[StefanScherer]

ping @mevatron :-)

[StefanScherer]

OK, I thought this wouldn't be that easy. /proc isn't fully available while building with qemu?

[StefanScherer]

green, merging for a pre-release

[mevatron]

@StefanScherer Awesome :) I had some difficulty getting the sysctl to ever automatically happen on boot-up. I would always have to manually enable the netfilter settings after logging in, so I switched over to the iptables fix that was recommended:

iptables -I INPUT -m conntrack --ctstate INVALID -j DROP

That has worked with no issues on my ODROID-XU4.

It'll be interesting if this works without a hitch on Blackbeard (nice codename by the way) :).

[StefanScherer]

@mevatron I had to revert this PR as sysctl doesn't work. Thanks for the iptables fix. I'll try to get this into v1.0.0