i40e: Fix for recent kernel panic

Whenever we get a Tx hang we issue a PFR, which means we send AQ
messages to VFS about the reset coming. Unfortunately with the recent
fix to be able to send messages to all VFS which earlier was not
happening at all we now are sending messages to not just the VFS that
are up but also to VFS that are not up.  AQ complains about this and
sends us an error in ARQ called LAN overflow event for a queue. We
check if the queue belongs to a VF and if it does we try to send a
vc_notify_vf_reset message to that VF. Well if the VF is not up/enabled
we will be entering this function with a non-active VF id. In this
function we were assuming VF struct is populated but it won't be if
the VF is not active.

Change-ID: Ic6733cda4582d3609fe6d83b2872bb2dcdc73f4a
Signed-off-by: Ashish N Shah <ashish.n.shah@intel.com>
Signed-off-by: Anjali Singhai Jain <anjali.singhai@intel.com>
Tested-by: Jim Young <jamesx.m.young@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>