Update frequency of WifiInfo upon connection or roam

This CL allows WifiStateMachine to update the frequency
field of WifiInfo upon connection event, supplicant
state changed event, and associated bssid event.

This also adds corresponding unit tests. In order to make
ScanDetailCache mockable, change the interesting methods to
explicit 'public'.

Bug: 64308543
Test: compile, unit tests

Change-Id: I4b886b2c81af1d4f17236d8413654c59cb102d10
3 files changed