MINOR: tevt/connection: Add dedicated termination events for lower locations

MINOR: tevt/connection: Add dedicated termination events for lower locations

To be able to add more accurate termination events for each location, the
enum will be splitted by location. Indeed, there are at most 16 possbile
events. It will be pretty confusing to use same termination events for the
different locations. So the best is to split them.

In this patch, the termination events for the fd, hs and xprt locations are
introduced. For now some holes are added to keep similar events aligned
across enums. But this may change in future.