Add callbacks for link layer and transport layer events

[emgre]

• See https://github.com/dnp3/opendnp3/blob/097b6ddcb012a54c9e8e10db03fec98ddc898341/cpp/lib/include/opendnp3/link/ILinkListener.h#L32-L52
• Callbacks must be able to collect these statistics: https://github.com/dnp3/opendnp3/blob/097b6ddcb012a54c9e8e10db03fec98ddc898341/cpp/lib/include/opendnp3/StackStatistics.h#L33-L79 but in a more versatile callback based approach.