Add getFrequency() to WifiInfoTest (along with other missing getters),
and test that it is consistent with ScanResult in ScanResultTest.
Test: atest android.net.wifi.cts.ScanResultTest
Fixes: b/138929469
Merged-In: I070b16661bc72a5c5035b0b227821b680d7d71ba
Merged-In: Ie99011acbbe66e9088f73964fd0c39d640594011
(cherry picked from commit 9c97c58656)
Change-Id: I83416c24c20c6774b2a66bf822419616f8cc5ab2