test/bonding: fix memory corruptions

test/bonding: fix memory corruptions

There were double-free problems in some test cases, which will cause
a duplicated mbuf will be added into mempool.  After double-free,
some new allocated mbuf will hold a same address and thus cause the
memory corruption.

Another minor issue is that in some test cases, allocated mbuf will
not be released after test case exits.  Hopefully these leaked mbuf
will be released by the next test case in its setup phase when
stopping the virtual pmd ports, while this do is a memory leak of
the exited test case.

To fix above 2 issues, this patch will do:
1) Release virtual pmd ports' tx queue in the clean up function
   remove_slaves_and_stop_bonded_device() of each test cases.
2) Do not release allocated mbufs for test bursts.  These mbufs
   will be released in remove_slaves_and_stop_bonded_device() when
   test case exits.

Fixes: 92073ef961ee ("bond: unit tests")

Signed-off-by: Herbert Guan <herbert.guan@arm.com>
Acked-by: Declan Doherty <declan.doherty@intel.com>