#75 Track unrecognized PDUs (issue #32)

This tracks the PDUs that are currently unrecognized and stores some information about the packets in a new table called 'unrecognized_pdus'. This information includes: 1. The source MAC-address. 2. The destination MAC-address. 3. The Ethertype number of the packet in decimal. 4. The number of occurrences of the packet. 5. The timestamp of the last occurrence of the packet. Furthermore, instead of spamming something like "Unknown PDU Type on L3: 29", it will print a message once that at least one unrecognized PDU was detected. Please let me know if these information are enough or if you can think of any improvements.(Preferably through email if there is something to improve) Or we'll just talk in the meeting about it.