realtek: l3: add a copyright line to l3.c and l3.h

Much of the L3 offload in these two files was written with AI
assistance, in the fixes and the IPv6 offload merged since September
2026. Add a copyright line for that work, naming the models that
assisted it, as the Assisted-by trailers of those commits do.

Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Gennaro Cimmino <gcimmino@rayonra.net>
Link: https://github.com/openwrt/openwrt/pull/25636
Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>

target/linux/realtek/files-6.18/drivers/net/dsa/rtl83xx/l3.c

@@ -1,4 +1,9 @@
 // SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2026 Gennaro Cimmino <gcimmino@rayonra.net>
+ * Assisted-by: Claude:claude-opus-5, Claude:claude-opus-5-5
+ */
+
 /*
  * Layer 3 unicast routing offload for the Realtek Otto switches
  *

target/linux/realtek/files-6.18/drivers/net/dsa/rtl83xx/l3.h

@@ -1,4 +1,8 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2026 Gennaro Cimmino <gcimmino@rayonra.net>
+ * Assisted-by: Claude:claude-opus-5, Claude:claude-opus-5-5
+ */
 
 #ifndef _OTTO_L3_H
 #define _OTTO_L3_H