ixgb: add explicit state checking

In order to remove the irq_sem code we need to implement strict
adapter state checking to prevent accidental double up or downs
or resets. This code is largely copied from e1000/e1000e.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>