service: fix loops to always scan all services

service: fix loops to always scan all services

Services can be registered and unregistered, and "holes" can
appear in the contiguous array of services if a service is
unregistered. As a result, we must never iterate to the
number of services (as counted by rte_service_count), instead
scanning the service array and checking if the service is valid.

After this commit, the rte_service_count variable is only used
for its intended purpose; tracking the number of services that
are present.

Fixes: 21698354c832 ("service: introduce service cores concept")

Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>
Acked-by: Pavan Nikhilesh <pbhagavatula@caviumnetworks.com>