wifi: rtw89: debug: extend dbgfs for MLO

Extend dbgfs vif/sta info to show current designated link.

Signed-off-by: Po-Hao Huang <phhuang@realtek.com>
Signed-off-by: Zong-Zhe Yang <kevin_yang@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20250505072440.45113-8-pkshih@realtek.com