realtek: dsa: rtl930x: write the source port field once

The encoder ORs the source port field twice: first the raw port, then
the value it composes from the trunk or stack device and the port. Both
land on the same ten bits, so what reaches the hardware is the two
values ORed together rather than the composed one.

For an entry that came from the decoder without a trunk the two agree,
because the decoder masked the port down to six bits and the composition
puts the stack device back above it. For a trunk entry the decoder
leaves the whole field in port and the composition rebuilds it from
trunk, so the first OR contributes bits the second does not, and the
entry is written with a source port that is neither.

Drop the first OR: the composition below covers both branches.

Compile-tested on realtek/rtl930x and realtek/rtl838x. Not exercised on
hardware: the driver writes no trunk entry of its own, and a trunk entry
read back and rewritten is the case this affects.

Assisted-by: Claude:claude-opus-5
Signed-off-by: Gennaro Cimmino <gcimmino@rayonra.net>
Link: https://github.com/openwrt/openwrt/pull/25220
Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>

target/linux/realtek/files-6.18/drivers/net/dsa/rtl83xx/rtl930x.c

@@ -524,7 +524,6 @@ static void rtl930x_fill_l2_row(u32 r[], struct rtl838x_l2_entry *e)
 	if (e->type == L2_UNICAST) {
 		r[2] |= e->is_static ? BIT(14) : 0;
 		r[1] |= e->rvid & 0xfff;
-		r[2] |= (e->port & 0x3ff) << 20;
 		if (e->is_trunk) {
 			r[2] |= BIT(30);
 			port = e->stack_dev << 9 | (e->port & 0x3f);