tg3: use random MAC address when tg3_get_device_address fails

Some of the tg3 NICs we use (BCM57762) reset the SRAM MAC address to the placeholder address on link flaps, tg3_chip_reset, etc. We've typically fixed it from userspace, but since e4c00ba7274b ("tg3: replace placeholder MAC address with device property") was merged, tg3 just fails probe as we don't have a way to get it through the generic device_get_mac_address infrastructure as fallback on our systems.

Make the driver assign a random address in this condition instead of being fatal for probe. Set deferred_probe_reason through dev_warn_probe if the address isn't yet available from the provider.

---
v4: use dev_warn_probe and the more compact calling form,
v3: https://lore.kernel.org/netdev/20260917223416.GA245819@visor/t/
handle EPROBE_DEFER, set deferred_reason through dev_err_probe,
v2: https://lore.kernel.org/netdev/20260914230521.GA1400582@visor/t/
assign random address instead of changing the logic in tg3_get_device_address,
v1: https://lore.kernel.org/netdev/20260903233255.GA4109366@visor/t/

---
 drivers/net/ethernet/broadcom/tg3.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

index 73a4b569b03e..6b8cb5b50f98 100644
@@ -17915,11 +17915,14 @@ static int tg3_init_one(struct pci_dev *pdev,
 
 	err = tg3_get_device_address(tp, addr);
 	if (err) {
-		dev_err(&pdev->dev,
-			"Could not obtain valid ethernet address, aborting\n");
-		goto err_out_apeunmap;
+		dev_warn_probe(&pdev->dev, err,
+			       "Could not obtain a valid ethernet address\n");
+		if (err == -EPROBE_DEFER)
+			goto err_out_apeunmap;
+		eth_hw_addr_random(dev);
+	} else {
+		eth_hw_addr_set(dev, addr);
 	}
-	eth_hw_addr_set(dev, addr);
 
 	intmbx = MAILBOX_INTERRUPT_0 + TG3_64BIT_REG_LOW;
 	rcvmbx = MAILBOX_RCVRET_CON_IDX_0 + TG3_64BIT_REG_LOW;

2.43.0