Wifi: Fix 2 ip addresses issue

Invoking the function clearInterfaceAddresses to clear
the initial IP first when change the "IP Settings"
for the select AP.

Change-Id: I38f6614e66cc3cf8d84e03c19d2d4badb1b16108
CRs-Fixed: 683307
NetworkManagementService: Change exception type thrown on IPv6

Changed the exception type thrown from IllegalStateException to
RemoteException whenever the IPv6 tethering rules fail to apply. The
IllegalStateException is not caught by the caller causing the JVM
to crash. By throwing RemoteException, the caller will catch and
print and error message instead of crashing.

CRs-Fixed: 662171
Change-Id: I92fadd43479a330f09bb20f699a4b9852123ab68