Go to the correct subscription in WifiCallingSettings

For subscriptions that support wifi calling, we have a preference on the
mobile network details page which leads to a Wifi Calling page. That
page already supports the concept of multiple subscriptions with a
header strip containing a tab for each subscription that supports wifi
calling. However, we were not necessarily selecting the *correct* tab
when going to this page. So you might be viewing the mobile network
details for subscription B and click on "Wifi Calling", only to land on
the page with the tab for subscription A selected.

This CL fixes the problem by adding an extra with the current
subscription id to the Preference's intent in
WifiCallingPreferenceController, and then reads that extra in
WifiCallingSettings and uses it to select the appropriate tab.

Fixes: 117135894
Test: make RunSettingsRoboTests
Change-Id: I3aec30072712247d14fe0fb6b61207535f9e981c