Connectivity: Add capability to allow tethering to use VPN upstreams [3/3]

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Author: Sam Mortimer <sam@mortimer.me.uk>
Date:   Thu Aug 15 19:40:55 2019 -0700

    fw/b: Add capability to allow tethering to use VPN upstreams

    * Toggled on/off at runtime via a new hotspot lineage setting.

    * Dynamically updates the tethering upstream for existing hotspot
      clients as VPNs are brought up / down or the hotspot setting
      is changed.

    * This implementation depends on fw/b config_tether_upstream_automatic
      being set to true.

    Change-Id: I2ac0b4acc0ea686dfdf54561cb3428808e337160

Change-Id: I2363e9baa007eac25be04ce23f0de41b80c5da42
2 files changed