Rename withIPv6AddrGenMode{Type}() methods to using{Type}MacAddress()

Callers of IpClient can tell it via the Builder whether a stable or
a random link-layer identifier is used.  IpClient will make the
appropriate IP-layer adjustments (for now this means RFC 7217
addresses or not).

Test: as follows
    - built
    - flashed
    - booted
    - runtest frameworks-net passes
    - ./frameworks/opt/net/wifi/tests/wifitests/runtests.sh runs as well
      as possible on AOSP (no new errors)
Bug: 62476366
Change-Id: Ic9d52ea4f2c6c3588852ed41c81f8664d5cc298a