p2p/nat: fix err shadowing in UPnP addAnyPortMapping (#33355)

The random-port retry loop in addAnyPortMapping shadowed the err
variable, causing the function to return (0, nil) when all attempts
failed. This change removes the shadowing and preserves the last error
across both the fixed-port and random-port retries, ensuring failures
are reported to callers correctly.

Author: Snezhkko

p2p/nat/natupnp.go

@@ -107,30 +107,30 @@ func (n *upnp) addAnyPortMapping(protocol string, extport, intport int, ip net.I
 		})
 	}
 	// For IGDv1 and v1 services we should first try to add with extport.
+	var lastErr error
 	for i := 0; i < retryCount+1; i++ {
-		err := n.withRateLimit(func() error {
+		lastErr = n.withRateLimit(func() error {
 			return n.client.AddPortMapping("", uint16(extport), protocol, uint16(intport), ip.String(), true, desc, lifetimeS)
 		})
-		if err == nil {
+		if lastErr == nil {
 			return uint16(extport), nil
 		}
-		log.Debug("Failed to add port mapping", "protocol", protocol, "extport", extport, "intport", intport, "err", err)
+		log.Debug("Failed to add port mapping", "protocol", protocol, "extport", extport, "intport", intport, "err", lastErr)
 	}
 
 	// If above fails, we retry with a random port.
 	// We retry several times because of possible port conflicts.
-	var err error
 	for i := 0; i < randomCount; i++ {
 		extport = n.randomPort()
-		err := n.withRateLimit(func() error {
+		lastErr = n.withRateLimit(func() error {
 			return n.client.AddPortMapping("", uint16(extport), protocol, uint16(intport), ip.String(), true, desc, lifetimeS)
 		})
-		if err == nil {
+		if lastErr == nil {
 			return uint16(extport), nil
 		}
-		log.Debug("Failed to add random port mapping", "protocol", protocol, "extport", extport, "intport", intport, "err", err)
+		log.Debug("Failed to add random port mapping", "protocol", protocol, "extport", extport, "intport", intport, "err", lastErr)
 	}
-	return 0, err
+	return 0, lastErr
 }
 
 func (n *upnp) randomPort() int {