examples/ip_pipeline: fix strict-aliasing

examples/ip_pipeline: fix strict-aliasing

Compile ip_pipeline in CentOS 6.5 with kernel 2.6.32-431
GCC 4.4.7, will lead below error:

    pipeline_routing_be.c: In function ‘pipeline_routing_msg_req_arp_add_handler’:
    pipeline_routing_be.c:1817: error: dereferencing pointer ‘({anonymous})’
				does break strict-aliasing rules

This because the code break strict-aliasing rule.
The patch solve this issue.

Fixes: 0ae7275810f1 (examples/ip_pipeline: add more functions to routing pipeline)

Signed-off-by: Michael Qiu <michael.qiu@intel.com>
Acked-by: Jasvinder Singh <jasvinder.singh@intel.com>