[rfc] lacp sysctl fixes

[Adrian Chadd]

Hi,

This patch introduces a few things:

* there's now an lacp node, under net.link.lagg.{unit}
* There's a strict mode parameter now
* There's now a debug node
* .. and rx_test/tx_test sit under that.

http://people.freebsd.org/~adrian/netflix/20130725-lacp-debugging-1.diff

It's a pre-requisite for shifting the LACP debug/trace calls into a
per-lacp instance and extending things to be slightly more useful.
Right now it's almost an all-or-nothing thing.

Thanks!


-adrian