TCP RTT in Frame metadata

[ayyaruq]

To enable more accurate latency tracking than simple ICMP echo requests, add the TCP RTT for each packet to the encapsulating Frame. This could get a bit weird with retransmitted Frames but still useful.

[ayyaruq]

This is actually way more complex than I thought, as the TCP context isn't passed through to the reassembler. Not actually sure the best way to do this other than either ignoring reassembly like Machina, or maybe implementing a custom protocol layer for Frames, but no clue how TCP reassembly would work with that.