zebra: local var in fpm_process_queue() sched cond

zebra: local var in fpm_process_queue() sched cond

Don't use an atomic operation to determine whether fpm_process_queue()
needs to be re-scheduled. Instead we can simply use a local variable
to determine if we stopped processing because we ran out of buffers.

In the case where we would have re-scheduled due to new context objects
in the queue (enqueued after we stopped processing), fpm_nl_process()
will schedule us (or will have done already).

Signed-off-by: Duncan Eastoe <duncan.eastoe@att.com>