Remove use of IOAddress::lessThan() from comparison operators

The IOAddress operators for < and <= use IOAddress::lessThan() rather than simply using the underlying data object, asio_address_'s operators as we already do for =. IOAddress::lessThan() adds an unnecessary layer of logic and uses a less efficient mechanism for comparison. Perflab testing demonstrated a modest improvement for v4 and a noticeable improvement for v6 (using memfile, persist, 1M clients no congestion).