Assert that RT_SCOPE_* and IFA_F_* are not zero.

If these constants are zero (or, rather, if they're not all
different), the test will fail with more cryptic error messages
whose cause is not obvious. Clearly check for that here.

Bug: 15602893
Change-Id: I7ca4a9c5e3d592fd93fbfa1b50666a1861a0031d