realtek: rtl931x: fix IPv4 unknown-mc portmask debug output

realtek: rtl931x: fix IPv4 unknown-mc portmask debug output

For the IPv4 unknown multicast flood portmask the first byte should be
for the higher port numbers and the following byte for the lower port
numbers, just like for the L2 unknown multicast flood portmask or the
IPv6 unknown multicast flood portmasks, too. Not the other way around.

Fix the debug output here by adjusting the offsets accordingly.

Fixes: 27029277f98d ("realtek: add switch driver support for the RTL93XX based switches")
Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>
Link: https://github.com/openwrt/openwrt/pull/21786
Signed-off-by: Robert Marko <robimarko@gmail.com>