Unfortunately sysprop - which is the SDK-compliant repacement for
SystemProperties - does not work properly in Android Q. Specificially
a java library is not generated and passed to the java compiler when
building ModemConfig. This works flawlessly in Android R.
Use SystemProperties from the private API as a stop-gap solution, until
we either pick a build-system fix or move to R.
Signed-off-by: Marijn Suijten <marijns95@gmail.com>