wifi: rtw89: 8852c: increase beacon loss to 6 seconds

Intermittent beacon loss from a specific AP causes the connection
to be lost. Increasing the beacon loss count can make the
connection more stable.

Signed-off-by: Kuan-Chung Chen <damon.chen@realtek.com>
Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Link: https://patch.msgid.link/20250606020302.16873-2-pkshih@realtek.com