Do not set AccessPoint.ssid to config.SSID for Passpoint networks

On each WifiTracker scan, existing Passpoint AccessPoints are updated
by update(config) with a WifiConfiguration returned by the framework
and then updated with fresh scan results through setScanResults().
Since the Passpoint WifiConfigurations given to update(config) have
null SSID, the call to setScanResults() sets the config.SSID to the
SSID of the strongest scan result. However, update(config) also sets
AccessPoint.ssid to config.SSID, which means the UI may display a blank
SSID before the call to setScanResults() sets it to the correct SSID.
Thus, update(config) should not set AccessPoint.ssid to config.SSID if
the AccessPoint is for Passpoint.

Bug: 137282522
Test: manual - connect to Passpoint network, validate SSID in network
details page.
Change-Id: I2218c1217de3e4fe48e40114a3ea8ceab3d845f2