selftests/bpf: make test_verifier run most programs

to improve test coverage make test_verifier run all successfully loaded
programs on 64-byte zero initialized data.
For clsbpf and xdp it means empty 64-byte packet.
For lwt and socket_filters it's 64-byte packet where skb->data
points after L2.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>