Fix min uid/gid allowed for child zygotes.

This should start at the app zygote isolated UID range, not the
regular isolated UID range.

Bug: 123758436
Test: atest CtsSeccompHostTestcases
      atest android.app.cts.ServiceTest#testActivityServiceBindingLru

Change-Id: Ic1b1ee02ab86a2e0f6a02525b466e6f5fdcdaf6c