Add getTetheredDhcpRanges() interface and call it before calling
mNwService.startTethering() to update dhcp ranges. This will allow p2p app
to run well concurrently with other tethering app(e.g. usb tethering).
Change-Id: I5e8ffeb5d2d396f48b897cd9396f133e25ecca57
Signed-off-by: Jianzheng Zhou <jianzheng.zhou@freescale.com>