net/nfp: fix mbufs releasing when stop or close

net/nfp: fix mbufs releasing when stop or close

PMDs have the responsibility of releasing mbufs sent through xmit burst
function. NFP PMD attaches those sent mbufs to the TX ring structure,
and it is at the next time a specific ring descriptor is going to be
used when the previous linked mbuf, already transmitted at that point,
is released. Those mbufs belonging to a chained mbuf got its own link
to a ring descriptor, and they are released independently of the mbuf
head of that chain.

The problem is how those mbufs are released when the PMD is stopped or
closed. Instead of releasing those mbufs as the xmit functions does,
this is independently of being in a mbuf chain, the code calls
rte_pktmbuf_free which will release not just the mbuf head in that
chain but all the chained mbufs. The loop will try to release those
mbufs which have already been released again when chained mbufs exist.

This patch fixes the problem using rte_pktmbuf_free_seg instead.

Fixes: b812daadad0d ("nfp: add Rx and Tx")
Cc: stable@dpdk.org
Signed-off-by: Alejandro Lucero <alejandro.lucero@netronome.com>