eal: reset lcore task callback and argument

eal: reset lcore task callback and argument

In the rte_eal_remote_launch function, the lcore function
pointer is checked for NULL. However, the pointer is never
reset to NULL. Reset the lcore function pointer and argument
after the worker has completed executing the lcore function.

Fixes: af75078fece3 ("first public release")
Cc: stable@dpdk.org
Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Reviewed-by: Ruifeng Wang <ruifeng.wang@arm.com>
Reviewed-by: Feifei Wang <feifei.wang2@arm.com>