kni: fix crash caused by freeing mempool
kni: fix crash caused by freeing mempool

To clean alloc_q, which has physical addresses of the mbufs, kni lib
free the pkt_mempool, but this leads a crash in kni unit test.

KNI library shouldn't free the pkt_mempool.

Implementation updated to find the mbufs in the alloc_q and return them
back to mempool.

Fixes: 8eba5ebd1811 ("kni: fix possible memory leak")
Cc: stable@dpdk.org

Signed-off-by: Ferruh Yigit <ba8734c3c506d2e3557bd4ac8fdaccd25bdb9aa7@intel.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk