kernel: backport rtl8365mb DSA driver improvements

kernel: backport rtl8365mb DSA driver improvements

Backport several fixes and enhancements for the rtl8365mb DSA driver
from upstream.

The backport includes the following changes:
- Fix for rtl8_4 tag (from v7.1)
- VLAN and Forwarding offload (from v7.2)

Before this backport, all bridge forwarding was handled by the CPU,
causing a significant performance drop between LAN ports, similar
to standard WAN/LAN routing. Enabling hardware forwarding offload
alleviates CPU overhead and restores line-rate switching performance.

Link: https://patch.msgid.link/20260408-realtek_fixes-v1-0-915ff1404d56@gmail.com
Link: https://patch.msgid.link/20260606-realtek_forward-v13-0-b9e409687cbe@gmail.com
Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/23738
Signed-off-by: Robert Marko <robimarko@gmail.com>