examples/l2fwd-event: clean up worker state before exit

examples/l2fwd-event: clean up worker state before exit

Event ports are configured to implicitly release the scheduler contexts
currently held in the next call to rte_event_dequeue_burst().
A worker core might still hold a scheduling context during exit, as the
next call to rte_event_dequeue_burst() is never made.
This might lead to deadlock based on the worker exit timing and when
there are very less number of flows.

Add clean up function to release any scheduling contexts held by the
worker by using RTE_EVENT_OP_RELEASE.

Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
Acked-by: Jerin Jacob <jerinj@marvell.com>