Support backward compatibility for restricted network permission

Some native daemons legacy design work with SYSTEM_UID. If none of
SYSTEM_UID apps declare the restricted network permission, it will
result in permission denial in daemons. Allow SYSTEM_UID in the
devices shipped before Q to support backward compatibility.

Bug:114245686
Test: 1. runtest frameworks-net
      2. atest FrameworksNetTests
      3. Native daemons with SYSTEM_UID can work normally

Change-Id: I6f3f0d83bcae74ef5389535b528af3baf649fa48