Transport: Change _currentAddresses from COWAL to standard ArrayList and lock

COWAL caused problems because replaceAddress() was removing the wrong address,
since RouterAddress.equals() does not compare caps, so empty '4' and '6' addresses would be equal.
So we could temporarily end up with multiple v4/v6 addresses.
COWAL wasn't really buying us anything anyway.

Fix removeAddress() that called the listener even if no change.