Disconnect network when captive portal returns unwanted.

When the user selects "Do not use this network" in the captive portal
app, it indicates that the user does not want to log in and does not
want to use the network. Thus, the network should be disconnected.

Internally handle the network disconnect in ConnectivityService upon
receiving a captive portal app response of APP_RETURN_UNWANTED.

Test: atest ConnectivityServiceTest
Change-Id: I789ddb663b533a71a77ed435fa91b0c20d3bbfd4
2 files changed