Clear calling identity

... after checking the caller. For hostside tests.

Fixes: 65245599
Test: cts-tradefed run singleCommand cts-dev -m CtsHostsideNetworkTests -t \
          com.android.cts.net.HostsideRestrictBackgroundNetworkTests

Change-Id: I094e38dbaf7818b9f645c55288bddffc879c6a0d