This changes the control_event_hs_descriptor_requested() call to add the hsdir
index optional value. v2 passes NULL all the time.
This commit creates hs_control.{c|h} that contains wrappers for the HS
subsystem to interact with the control port subsystem.
The descriptor REQUESTED event is implemented following proposal 284 extension
for v3.
Signed-off-by: David Goulet <dgoulet@torproject.org>
