samples: net: dumb_http_server: Add zero configuration

Adds zero configuration based on LLMNR. This should be working in
Windows out of the box, zephyr can be accessed with http://zephyr/

.
Can be combined with netusb configuration (RNDIS is supported in
Windows).

Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@intel.com>