Add a new type of frame, for the event that should be registered by the
event logger.

The event logger does not exist yet, but in the future, the simulated
nodes will be able to reach for such an entity on order to log special
events (e.g. node joins simulation, node authenticates to its neighbor,
etc.)
Bugfix: frame sent by nodes are now received in their entirety
Pcap-dumper now stores the sender's frame in the associated pcap file

The previous behavior was to only register the frame that were received
by the node. Because the frame sent by the node were not recorded, it
was actually difficult to analyse the capture file.
Remove the (new) timestamp field before processing the 15.4 frame
Wiredto154 sends a "simulation end" frame to all the nodes upon exit
(thus ending the simulation for them)
extend the command line of wiredto154 to pass a different multicast
address and port