nn_queue.h: move metadata functions to metadata.{c,h}
nn_queue.h: move metadata functions to metadata.{c,h}

megahall/sdn_sensor,TidyHuang/sdn_sensor,megahall/sdn_sensor,TidyHuang/sdn_sensor,TidyHuang/sdn_sensor,megahall/sdn_sensor,megahall/sdn_sensor,megahall/sdn_sensor,megahall/sdn_sensor,TidyHuang/sdn_sensor,megahall/sdn_sensor,TidyHuang/sdn_sensor,TidyHuang/sdn_sensor,megahall/sdn_sensor,TidyHuang/sdn_sensor,TidyHuang/sdn_sensor