igb: save and restore pcie/msi state to support EEH recovery

To enable EEH support for pci-express network adapters, pcie/msi state
needs to be saved and restored for that adapter.

[after similar patches for ixgbe and e1000e from Wendy Xiong]

Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
Cc: Wendy Xiong <wendyx@us.ibm.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>