igc: fix a log entry using uninitialized netdev

During successful probe, igc logs this:

[    5.133667] igc 0000:01:00.0 (unnamed net_device) (uninitialized): PHC added
                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The reason is that igc_ptp_init() is called very early, even before
register_netdev() has been called. So the netdev_info() call works
on a partially uninitialized netdev.

Fix this by calling igc_ptp_init() after register_netdev(), right
after the media autosense check, just as in igb.  Add a comment,
just as in igb.

Now the log message is fine:

[    5.200987] igc 0000:01:00.0 eth0: PHC added
Signed-off-by: Corinna Vinschen <vinschen@redhat.com>
Reviewed-by: Hariprasad Kelam <hkelam@marvell.com>
Acked-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
Tested-by: Naama Meir <naamax.meir@linux.intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/igc/igc_main.c

@@ -7028,8 +7028,6 @@ static int igc_probe(struct pci_dev *pdev,
 	device_set_wakeup_enable(&adapter->pdev->dev,
 				 adapter->flags & IGC_FLAG_WOL_SUPPORTED);
 
-	igc_ptp_init(adapter);
-
 	igc_tsn_clear_schedule(adapter);
 
 	/* reset the hardware with the new settings */
@@ -7051,6 +7049,9 @@ static int igc_probe(struct pci_dev *pdev,
 	/* Check if Media Autosense is enabled */
 	adapter->ei = *ei;
 
+	/* do hw tstamp init after resetting */
+	igc_ptp_init(adapter);
+
 	/* print pcie link status and MAC address */
 	pcie_print_link_status(pdev);
 	netdev_info(netdev, "MAC: %pM\n", netdev->dev_addr);