realtek: rtl931x: Fix VLAN tagging and untagging

realtek: rtl931x: Fix VLAN tagging and untagging

* In RTL931x, bit 31 of the (4th column) of 802_1Q_VLAN_QINQ table
  indicates the validity of l2 tunnel. Before bit 63 (3rd column)
  was being checked for validity of l2 tunnel.

* The untagged_ports requires 64 bits to represent 56 ports. Do not
  store u64 in u32 variable

* First 24 ports are represented in the 2nd register not just first 20

Signed-off-by: Harshal Gohel <hg@simonwunderlich.de>
Signed-off-by: Sharadanand Karanjkar <sk@simonwunderlich.de>
Link: https://github.com/openwrt/openwrt/pull/19576
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>