Determine an appropriate value (if any) for delaying the 2nd packet on a path

[WesleyRosenblum]

In #1042 we introduced a 10ms delay on the 2nd packet in a path, based on evidence that pacing the 2nd packet can improve loss. #1052 set that delay to 0 until we can evaluate an appropriate value for the delay. This task is to perform that evaluation and set the delay to a value that improves packet loss to a degree that it is worth the delay. One possible outcome is that no delay is worth it due to improvements in network routers, and thus the feature should be removed.