Improve portblock to use conntrack

[jarrpa]

As a followup to #1, improve the portblock RA to use conntrack to track TCP connections for tickling rather than flat files populated via netstat.

[guihecheng]

@jarrpa AFAIK, conntrackd may not be ready for an Active/Active setup ?

[jarrpa]

@guihecheng Oh? Is there something that says as much, whether an official statement or some testing someone has done?

[guihecheng]

@jarrpa hmmm... not really, I've searched a lot, but only some old mail threads found, there seems to be a basic support but no idea whether the feature is stable or not.
There is also a conntrackd RA which is in Master/Slave mode, but not Active/Active.
Maybe I shall try that a bit myself ;)