Make circ_times static, and abstract most of its accessors.
The circ_times structure is exported as a global from circuitbuild.c. It really shouldn't be. It has 3 kinds of external users FWICT:
- Things that pass it as an argument to circuit_build_*().
- Two functions in circuituse.c that want to know the current timeout values.
For the former we could use an accessor function, or we could have the functions in circuitbuild.c use the static object if they receive NULL. For the latter, we could have a function that returns the current timeouts.
Making this change would also let us more completely avoid looking at circ_times when LearnCircuitBuildTimeout is 0.