Fix bug of Wi-Fi configuration page which was involved by the MTK patch.

Merge from HC5761.

Added nathelper-extra and rename 'p2pvtun' to 'minivtun'.

Use 'broadcom' type to cheat LuCI for correct configuration.

Fix the patch to enable ePA to boost 2.4G signal.

Allow developer to attach customized configuration items with file .c…

…onfig.extra.

config-xiaomi-mini: Updated from 'make menuconfig' result.