examples/ip_pipeline: remove check of null response

examples/ip_pipeline: remove check of null response

For sending request messages to data plane threads, the
caller invokes *_msg_send_recv() functions which never
return null response. Thus, removed redundant check on
the returned response.

Coverity issue: 357750, 357740, 357749, 357758, 357702, 357736
Coverity issue: 357679, 357791, 357738, 357778, 357716, 357705
Coverity issue: 357776, 357753, 357729, 357735, 357773, 357723
Fixes: 32e5d9b154cb ("examples/ip_pipeline: add enable and disable commands")
Fixes: 50e73d051806 ("examples/ip_pipeline: add stats read commands")
Fixes: 6b1b3c3c9d30 ("examples/ip_pipeline: add port enable and disable commands")
Fixes: a3a95b7d58b9 ("examples/ip_pipeline: add table entry commands")
Fixes: 3186282f8e12 ("examples/ip_pipeline: add table bulk add command")
Fixes: f634e4c5698a ("examples/ip_pipeline: add table entry delete command")
Fixes: c64b9121a963 ("examples/ip_pipeline: add table entry stats command")
Fixes: 7e11393e40ef ("examples/ip_pipeline: add meter profile commands")
Fixes: e92058d604e6 ("examples/ip_pipeline: add meter stats command")
Fixes: 2b82ef4861c0 ("examples/ip_pipeline: add DSCP table update command")
Fixes: d0d306c7f2a1 ("examples/ip_pipeline: add TTL stats command")
Fixes: a3169ee5ec59 ("examples/ip_pipeline: support rule time read")
Cc: stable@dpdk.org
Signed-off-by: Jasvinder Singh <jasvinder.singh@intel.com>
Acked-by: Cristian Dumitrescu <cristian.dumitrescu@intel.com>