WifiNetworkFactory: Always pick bssid & disable fw roaming

Changes:
a) Disable firmware roaming for all connections intitiated by the
network request API by force selecting a BSSID.
b) If there are multiple BSSIDs matching the user selected network, pick
the one with the best rssi.

Test: act.py -c wifi_manager_cross.config -tb dut-name -tc
WifiNetworkRequestTest
Test: atest com.android.server.wifi

Change-Id: I71e45a4eddbd7b4d4a068b94ae8ba1a93bc9cd90
2 files changed