Allow dlopen()ing libraries from the netd APEX.

This is a workaround to allow us to use libnetd_resolv.so from
the resolver APEX before b/120661824 is fixed.

We cannot put the APEX into the search path due to b/120661824,
but we can put it into the permitted path,

Test: builds, boots
Test: system/netd/tests/runtests.sh
Test: atest FrameworksNetTests android.net.cts.ConnectivityManagerTest
Change-Id: Ia68df860b7edc92180284f62736146e6029d7655