[c-nsp] BFD on port channel

[Oliver Boehmer (oboehmer)]

Geert,

> 
> so no, forget BFD and portchannels :-)
> 

not so quickly :-) On NX-OS as well as IOS-XR, two platforms/OS where we
have been running BFD sessions on the linecards, we do support BFD on
channels/bundle, albeit in a proprietary fashion as this is not (yet?)
standardized. As we're still using Layer 3 BFD pkts, now running over
each bundle/channel member, the topologies supported by the specific BFD
over channel implementations are limited, on IOS-XR we can only do
back-to-back bundles (i.e. between two XR devices), NX-OS is a bit more
flexible in this regard. 

So BFD and portchannels is still tricky and limited to some platforms
and topologies, but it's certainly not impossible. 

	oli