net/iavf: fix crash after VF reset failure

net/iavf: fix crash after VF reset failure

Some pointers will be set to NULL when iavf_dev_reset() failed,
for example vf->vf_res, vf->vsi_res vf->rss_key and etc.
APIs access these NULL pointers will trigger segfault.

This patch adds closed flag to indicate that the VF is closed,
and rejects API calls in this state to avoid coredump.

Fixes: e74e1bb6280d ("net/iavf: enable port reset")
Cc: stable@dpdk.org
Signed-off-by: Yiding Zhou <yidingx.zhou@intel.com>
Acked-by: Qi Zhang <qi.z.zhang@intel.com>