hotspot2: cleanup ANQPParser

Below is the list of cleanups:
- removed unused function
- cleaned up parsing of vendor specific element
  - only support Hotspot 2.0 elements, since these are the only
    elements that we cared about
- added unit tests

Bug: 33000864
Test: frameworks/opt/net/wifi/tests/wifitests/runtests.sh
Change-Id: I2e492525dfa5e28c12336e2bbec2f2882e0af57c
3 files changed
tree: 28cd615b069a2127b828205b44663ce0914546e0
  1. libwifi_hal/
  2. libwifi_system/
  3. service/
  4. tests/
  5. PREUPLOAD.cfg