ixgbe: Additional adapter removal checks

Additional checks are needed for a detected removal not to cause
problems. Some involve simply avoiding a lot of stuff that can't
do anything good, and also cases where the phony return value can
cause problems. In addition, down the adapter when the removal is
sensed.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>