selftests/bpf: use proper type when passing prog_type

Use bpf_prog_type instead of bpf_map_type when passing prog_type.

-Wenum-conversion might be unhappy about it:
	error: implicit conversion from enumeration type
	'enum bpf_map_type' to different enumeration type
	'enum bpf_prog_type'

Signed-off-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>