Rob added code to let you put plab nodes in a LAN (with protocol "ipv4")
so that the LAN could be traced.

Meanwhile, Leigh has been adding completion events for various event types
and creating various combo event groups for addressing all elements of a LAN,
all LANs, etc.

For pelab we have a link "reset" event which is sent to the "__all_lans"
event group to reset the shaping of all links/lans.  Unfortunately, plab
nodes don't run a delay agent, so link events sent there fall on deaf ears.

Ergo, the event scheduler waits for completions from all agents it send
the "reset" to, but the plab nodes will never respond since there are no
link agents.