realtek: rtl93xx: fix incorrect destination port selection

realtek: rtl93xx: fix incorrect destination port selection

When testing LLDP and STP, we observed that locally generated multicast
packets (e.g. LLDP, STP) were not restricted to the designated output
port(s). For example, when transmitting on `lan1`, the same packet was also
forwarded to other ports such as `lan2`.

Steps to reproduce:

1. Configure lldpd to use `lan1` in UCI and restart the service
2. Connect devices to `lan1` and `lan2`
3. Observe that the device on `lan2` still receives LLDP packets

The issue was caused by an incorrect `FWD_TYPE` setting in the TX CPU TAG,
which failed to enforce the selected egress port(s).

Fix this by updating the TX CPU TAG to set `FWD_TYPE` correctly, ensuring
that locally generated packets are transmitted only on the intended
port(s).

Signed-off-by: Issam Hamdi <ih@simonwunderlich.de>
Link: https://github.com/openwrt/openwrt/pull/19802
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>