selftest/bpf: Get rid of a bunch of explicit BPF program type setting

Now that libbpf can correctly guess BPF program types from section
names, remove a bunch of explicit bpf_program__set_type() calls
throughout tests.

Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20191021033902.3856966-8-andriin@fb.com