Incorrect ipv6 hostaddress format in events.

Currently when bootstrap is stuck, tor reports hostaddr in an event to the control port. The hostaddr string is malformed for ipv6, which is ip:port without the bracket notation. The problematic code I can find is tor/src/ feature/control/control_bootstrap.c, in function control_event_bootstrap_problem at line 268. I fear the same might happen somewhere else in the code.