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

BugLink: https://bugs.launchpad.net/bugs/1806818

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 subsytem 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>
(cherry picked from commit c881c486761fd093d104fa86e373e504aa60f35e git://git.kernel.org/pub/scm/linux/kernel/git/jkirsher/next-queue.git dev-queue)
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Acked-by: Kleber Souza <kleber.souza@canonical.com>
Acked-by: Seth Forshee <seth.forshee@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/net/ethernet/intel/igb/igb_main.c

@@ -7426,9 +7426,11 @@ static int __igb_shutdown(struct pci_dev *pdev, bool *enable_wake,
 	rtnl_unlock();
 
 #ifdef CONFIG_PM
-	retval = pci_save_state(pdev);
-	if (retval)
-		return retval;
+	if (!runtime) {
+		retval = pci_save_state(pdev);
+		if (retval)
+			return retval;
+	}
 #endif
 
 	status = rd32(E1000_STATUS);