Make Wifi WPS API available on application layer

Un-hide WPS methods (and required interface classes, etc.) of WifiManager to
enable Apps to start/stop the WPS procedure, add a patch for WPS method
KEYPAD to avoid early failure callbacks. (Methods PBC, DISPLAY, KEYPAD
tested on 4.4.2_r2.)

Change-Id: I25aafdc4b637c87d754d4fdb70e40a34a569b738
Signed-off-by: Olaf Stoyke <o.stoyke@avm.de>