examples/l2fwd-event: fix event device config

Always enable implicit release since we don't support explicit release
in datapath.
Master lcore is used only for printing stats so don't allocate event
port for it.
Fix service launch for event device without distributed scheduling.

Fixes: bcb6f841d42a ("examples/l2fwd-event: setup service core")
Cc: stable@dpdk.org
Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>