hmland: don't impersonate HM-CFG-LAN by default.

Don't respond to K-commands with HM-LAN-IF by default but respond with
the actual string returned by the USB device (HM-USB-IF). This breaks
compatibility with Fhem-versions before 2015-06-19 and possibly other
software (Homegear, eQ-3 rfd). To restore compatibility with these
software-packages, add the new command-line switch "-I" which restores
old behaviour.