This contains the following changes:
1. Make NETWORK_AVOID_BAD_WIFI a tristate: 0 means never avoid
bad wifi, unset means prompt the user, 1 means always avoid.
2. Look at NETWORK_AVOID_BAD_WIFI only if the carrier restricts
avoiding bad wifi (previously, we relied on the setting being
null and defaulting to the value of the config variable).
3. Add an avoidUnvalidated bit to NetworkAgentInfo to track
whether the user has requested switching away from this
unvalidated network even though avoiding bad wifi is generally
disabled. This is set to true when the user selects "switch"
in the dialog without setting the "Don't ask again" checkbox.
4. Add a hidden setAvoidUnvalidated API to ConnectivityManager to
set the avoidUnvalidated bit.
5. Additional unit test coverage.
Bug: 31075769
Change-Id: I1be60c3016c8095df3c4752330149ce638bd0ce1
165c51c0eb