Replace the way to access StaticIpConfiguration

StaticIpConfiguration is a part of incoming connectivity
mainline module. The hidden variable is not accessible for
module outside. The caller should use getter and builder
to access it. Replace the usage with the formal way.

Test: make RunSettingsRoboTests ROBOTEST_FILTER=\
      com.android.settings.wifi.WifiConfigControllerTest
Test: make RunSettingsRoboTests ROBOTEST_FILTER=\
      com.android.settings.wifi.WifiConfigController2Test
Change-Id: I2ccd427ba19a4ec7df863c38ee0b34cf0be87fa5