net/ena: fix cleanup of the Tx bufs

net/ena: fix cleanup of the Tx bufs

After cleanup of the mbuf on Tx path, queue was still pointing to this
mbuf and upon cleanup of the Tx buffers, it was being freed second time.

Moreover, to make sure that upon interrupt all mbufs will be freed,
whole ring is being cleaned up instead of part of it - originally only
range between head and tail was being cleaned up.

Fixes: 1173fca25af9 ("ena: add polling-mode driver")
Cc: stable@dpdk.org
Signed-off-by: Michal Krawczyk <mk@semihalf.com>