igb: Fix an issue that PME is not enabled during runtime suspend

I210 ethernet card doesn't wakeup when a cable gets plugged. It's
because its PME is not set.

Since commit 42eca230 ("PCI: Don't touch card regs after runtime
suspend D3"), if the PCI state is saved, pci_pm_runtime_suspend() stops
calling pci_finish_runtime_suspend(), which enables the PCI PME.

To fix the issue, let's not to save PCI states when it's runtime
suspend, to let the PCI subsystem enables PME.

Fixes: 42eca230

 ("PCI: Don't touch card regs after runtime suspend D3")
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>