app/test: check for mbuf allocation failure

app/test: check for mbuf allocation failure

If mbuf allocation failed for whatever reason, we would get a NULL
pointer exception in test_table_acl.c:test_pipeline_single_filter test
case.
We fix this by causing an early break out of the application loop. If we
quit the test immediately we would leak any existing allocated mbufs,
but by breaking instead, we allow the test to continue and clean up the
mbufs already in the pipeline, while still having a test failure as the
mbuf counts should not match.

Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>