Automatically add broadcast known_host nodes for interfaces

[kivkiv12345]

I.e:

csp add zmq 30 localhost
# ZMQ0 is added
ping ZMQ0-broadcast
# Pings 63

Dual-can could be explicitly supported by finding a common prefix for interfaces on the same subnet:

csp add can -c can0 30
# CAN0 is added
csp add can -c can1 30
# CAN1 is added
# "CAN" is the common prefix
ping CAN-broadcast
# Pings node 63

Perhaps the known_host names should be .lower()'ered as well.