classic protocol could not handle shortcuts. Is necessary for bootstrap

see redmine: https://dev.cfengine.com/issues/3697
I just noticed, ```conn->revdns``` is only set for the new protocol (see server.c:386) so in classic_protocol.c it is always an empty string. The old protocol never does reverse DNS lookup, it instead trusts what the client declares as its hostname, use ```conn->hostname``` in all the cases.