Fix NPE in ConnectivityService

Could occur when requestRouteToHostAddress is called on a network
with no associated tracker.  Code later in the method handles
this case gracefully but code introduced in JB throws an exception.

Change-Id: I6c8a0e313ecbcca120aeb5dd0802a72114749aa1
Merge "Fix NPE in ConnectivityService" into kk4.4