tests: gif(4): Add tests to cover all IPv[46] in IPv[46] setups

While here, rename basic to 4in4 to be consistent with other tests.

MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D51566

(cherry picked from commit 62439516cc9bba32ed2406f340326c4d37e4cc59)
(cherry picked from commit c2806cddc64766b69daa42b4fb192f767e4b4705)