Restore legacy types when registering mobile requests

Test: as follows
    - built (bullhead)
    - flashed
    - booted
    - runtest frameworks-net passes
    - vanilla wifi to mobile tethering (no DUN)
    - tested with DUN by:
        - adding "dun" to the APN type
        - adb shell settings put global tether_dun_required 1
        - verified the bug exists without this fix
Bug: 32163131
Bug: 34364553
Change-Id: Idf1a9a2c8191c40abed29e1789f62aefb83ed1ce