add missing sysctl parameter

[rndmh3ro]

Fixes #115

[ypid]

Not sure about martian off the top of my head. Maybe others know this without looking it up.

[rndmh3ro]

A martian packet is a packet with a source address which is obviously wrong - nothing could possibly be routed back to that address.

See:
https://serverfault.com/questions/570980/what-is-the-usefulness-of-logging-of-martians-packet
https://en.wikipedia.org/wiki/Martian_packet

This PR just tries to make the handling of martians consistent, we already set this parameter for all network interfaces (here), this just adds the setting for the default interface.

BTW thanks for taking the time to review everything so thoroughly!

[rndmh3ro]

I will add more sysctl-parameters that are missing to this PR.

[ypid]

You are welcome :) I will look into this when I start using the role. Will probably take a while.

[burdena]

I was about to create my own pull request for net.ipv4.conf.default.log_martians glad someone else already spotted it. Just to add to its need/requirement, the Inspec test currently checks for it https://github.com/dev-sec/linux-baseline/blob/master/controls/sysctl_spec.rb#L196. Hope this helps getting the PR progressed.

[atomic111]

@rndmh3ro thanks for your great work!!!