Allow GuardMgr to expose bridges as guards (part 1)
This branch lays more groundwork for GuardMgr to make FirstHopId
more robust, to give out FirstHop
objects that are bridges internally, and for CircMgr to use them in multihop circuits even if they are not listed in the NetDir
.
Not yet implemented here:
- Actually choosing bridges as guards when using the "bridges" guard-sample.
- Switching to the "bridges" guard-sample when configured to do so.