Adding the Destination to ExtendedData of ext_iface_processor.cpp
Adding the Destination to ExtendedData of ext_iface_processor.h

Messages forwarded by the external interface processor (ExtIfaceProcessor) elide the destination and just forward the source, length(of the payload), the payload itself and optionally Extended Data with locally calculated link metric. Without the destination transferred, the addressed nodes cannot distinguish between broadcast or unicast. Therefor I added the destination address id to the Extended Data.
Merge pull request #1 from MarcStelzner/master

Adding a new field "destination_" including getter/setter to the ExtendedData