InterfaceUpdated() writes reverseContext and reverseCancel without
synchronization while connectorLoop/connectorConnect goroutines
read them concurrently. close() also accesses reverseCancel without
a lock.
Fix by extending reverseAccess mutex to protect these fields:
- Add getReverseContext()/resetReverseContext() methods
- Pass context as parameter to connectorConnect
- Merge close() into a single lock acquisition
- Use resetReverseContext() in InterfaceUpdated()
3b177df05e