net: dns: Log with debug level instead of error level when recv fails

This condition can happen if there is MDNS activity on the network that is
either not according to specifications or not supported by Zephyr.

Lowering the log level from ERR to DBG, since this does not indicate an
error in the Zephyr application.

Signed-off-by: Helge Juul <helge@fastmail.com>