Due to the property trigger on persist.sys.usb.config,
setting the default function also sets the current function.
Now we combine both of these methods into setCurrentFunction, which has
a "makeDefault" option to make the new function the default.
This change should eliminate some problems with setting properties due to
multiple property triggers happening at the same time.
Change-Id: I9851299e9c2ee20475eada1a8104c0d50bf5a9e1
Signed-off-by: Mike Lockwood <lockwood@android.com>