The Rx adapter stop call does not guarantee that the
SW service function will not execute after the
rte_event_eth_rx_adapter_stop() call.
Add a "started" flag to prevent the adapter from executing
if stop has been called.
Fixes: 9c38b704d280 ("eventdev: add eth Rx adapter implementation")
Cc: stable@dpdk.org
Signed-off-by: Nikhil Rao <nikhil.rao@intel.com>