ixgbe: In SR-IOV mode insert delay before bring the adapter up

VFs running in guest VMs do not respond in as timely a manner to
PF indication it is going down as they do when running in the host
domain.  If the adapter is in SR-IOV mode insert a two second delay
to guarantee that all VFs have had time to respond to the PF reset.
In any case resetting the PF while VFs are active should be
discouraged but if it must be done then there will be a two
second delay to help synchronize resets among the PF and all the
VFs.

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>