service: use log for error messages

service: use log for error messages

EAL should always use rte_log instead of putting errors to
stderr (which maybe redirected to /dev/null in a daemon).

Also checks for null before rte_free are unnecessary.
Minor code consistency improvements.

Fixes: 21698354c832 ("service: introduce service cores concept")
Cc: stable@dpdk.org
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Harry van Haaren <harry.van.haaren@intel.com>
Acked-by: Harry van Haaren <harry.van.haaren@intel.com>