[real] do not wait for extaddr change from real devices (#51)
[real] do not wait for extaddr change from real devices (#51)

Some background on why OTNS expects the node to send extaddr status
right after node being created:

This feature was added when Virtual Time UART was supported by #5

OT Simulation that uses Virtual time UART receives/sends CLI
input/output via UDP events, instead of stdin/stdout.  After the node
is created, OTNS needs to send CLI commands to it immediately,
e.g. mode rsdn, thread start, etc. But it is likely that the
simulation instance has not opened the UDP port for receiving UDP
messages and thus the CLI commands could be lost. So, OTNS needs a way
to know that the node is ready for receiving UDP messages before
sending any CLI commands. A simple and straightforward way of doing
this is by receiving any UDP message from the node.  Since extaddr
status is the first UDP message and is always sent (to my
observation), OTNS waits for the extaddr event to come.

This however isn't true for Silk devices.
openthread/ot-ns,openthread/ot-ns,openthread/ot-ns,openthread/ot-ns,openthread/ot-ns