ice: Protect vf_state check by cfg_lock in ice_vc_process_vf_msg()

Previous patch labelled "ice: Fix incorrect locking in
ice_vc_process_vf_msg()"  fixed an issue with ignored messages
sent by VF driver but a small race window still left.

Recently caught trace during 'ip link set ... vf 0 vlan ...' operation:

[ 7332.995625] ice 0000:3b:00.0: Clearing port VLAN on VF 0
[ 7333.001023] iavf 0000:3b:01.0: Reset indication received from the PF
[ 7333.007391] iavf 0000:3b:01.0: Scheduling reset task
[ 7333.059575] iavf 0000:3b:01.0: PF returned error -5 (IAVF_ERR_PARAM) to our request 3
[ 7333.059626] ice 0000:3b:00.0: Invalid message from VF 0, opcode 3, len 4, error -1

Setting of VLAN for VF causes a reset of the affected VF using
ice_reset_vf() function that runs with cfg_lock taken:

1. ice_notify_vf_reset() informs IAVF driver that reset is needed and
   IAVF schedules its own reset procedure
2. Bit ICE_VF_STATE_DIS is set in vf->vf_state
3. Misc initialization steps
4. ice_sriov_post_vsi_rebuild() -> ice_vf_set_initialized() and that
   clears ICE_VF_STATE_DIS in vf->vf_state

Step 3 is mentioned race window because IAVF reset procedure runs in
parallel and one of its step is sending of VIRTCHNL_OP_GET_VF_RESOURCES
message (opcode==3). This message is handled in ice_vc_process_vf_msg()
and if it is received during the mentioned race window then it's
marked as invalid and error is returned to VF driver.

Protect vf_state check in ice_vc_process_vf_msg() by cfg_lock to avoid
this race condition.

Fixes: e6ba5273 ("ice: Fix race conditions between virtchnl handling and VF ndo ops")
Tested-by: Fei Liu <feliu@redhat.com>
Signed-off-by: Ivan Vecera <ivecera@redhat.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Konrad Jankowski <konrad0.jankowski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>