net/i40e: fix virtchnl message response timeout

PF driver and VF driver communicated with each other by virtual
channel message. When VF sends message to PF to enable some
offload capability, PF should response if it is successful or not.
VIRTCHNL_OP_ENABLE_VLAN_STRIPPING is a new added message and the
old PF driver doesn’t support that. So no response is received by
DPDK VF. Then VF is blocked on this message and cannot roll back.
This patch clears pending command on VF side when the waiting duration
expires to avoid blocking following communication.

Fixes: 5f0b95d59a98 ("net/i40e: support VLAN stripping for VF")
Cc: stable@dpdk.org
Signed-off-by: Beilei Xing <beilei.xing@intel.com>