Use embedded native libs for NetworkStack.apk.

So that the /system version of NetworkStack.apk can be re-installed on
/data without causing problems. This is useful for testing and necessary
for supporting rollback to the system version of NetworkStack.apk.

Bug: 131703417
Bug: 132195177
Test: Confirm NetworkStack.apk now includes .so files.
Test: adb install --staged NetworkStack.apk
      adb reboot
      Device reboots without problems.

Change-Id: I7c9a1702a2c18e0333b5e409f04b7658fe685f97