framework-wifi-util-lib: compile against min_sdk_version = 30

sdk_version should still be module_current since we need to use
new Android S APIs. Change min_sdk_version to 30 to satisfy
Mainline module requirements.

Bug: 171330443
Test: compiles
Change-Id: I1129f690b06e7da8b3b8bbd60ab82253d52e75f8