ixgbe: Improve reset coordination between the PF and the VF

Inadequate coordination between the PF driver and the VF driver results
in tx hangs in the VF driver when you perform certain actions that will
lead to a re-init of the PF.  Add feature to notify active VFs when the PF
is about to re-initialize so that the VFs can take appropriate action.

Signed-off-by: Greg Rose <gregory.v.rose@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>