mkimg.sh: add androidboot.wificountrycode=US to kernel cmdline

The ro.boot.wificountrycode property is a ro.boot.* namespace property
that can ONLY be populated from the kernel cmdline (androidboot.xxx).
Setting it in vendor.prop had no effect — the value stayed '00'.

This caused the WiFi regulatory domain to default to 'country 00'
(world), which forced passive scanning on all 5GHz channels and
capped TX power at 3 dBm.  On a DFS channel this meant 60s CAC
delays, failed scans, and crippled TX power causing SAE handshake
failures.

This is the actual fix — adding the boot parameter that the WiFi
framework reads to set the regulatory domain via nl80211.
Users in other regulatory domains should edit this line.

mkimg.sh

@@ -142,7 +142,7 @@ label LineageOS Android TV
     kernel /Image
     fdt /rk3588-orangepi-5-ultra.dtb
     initrd /ramdisk.img
-    append console=ttyS2,1500000 no_console_suspend root=/dev/ram0 rootwait androidboot.hardware=tart androidboot.selinux=permissive androidboot.boot_devices=fe2c0000.mmc androidboot.console=ttyS2
+    append console=ttyS2,1500000 no_console_suspend root=/dev/ram0 rootwait androidboot.hardware=tart androidboot.selinux=permissive androidboot.boot_devices=fe2c0000.mmc androidboot.console=ttyS2 androidboot.wificountrycode=US
 EXTLINUX_EOF
 sudo cp ${KERNEL_PATH}/boot.scr "${BOOT_MOUNT}/"
 sudo cp ${KERNEL_PATH}/android-sdcard.dtbo "${BOOT_MOUNT}/"

vendor.prop

@@ -81,7 +81,7 @@ persist.device_config.mglru_native.lru_gen_config=core
 ro.boot.hypervisor.vm.supported=1
 
 # Wifi
-ro.boot.wificountrycode=US
+ro.boot.wificountrycode=00
 wifi.interface=wlan0
 
 # Window extensions