Pass in the netId using intent data, not intent extras.

This allows ConnectivityService to use different PendingIntents
for different dialogs; two PendingIntents that differ in their
data are treated as different, but two PendingIntents that differ
only in their extras are treated as being the same.

Bug: 20081183
Change-Id: Ie1bdcf2a0a0747be815ea528db0cb34f5ab415b9