Always set the usb config when modifying it.

On some devices, setting system properties takes too long and we end up
with races where adbd gets killed and never comes back. With this
change we avoid a small optimization that checks the previous value of
the config, instead opting to set it every time.

Bug: 23631400
Change-Id: I7567cc2efb3d5d15c45334bd66b28877a2af0ac3