bpf: Refactor and bug fix in test_func_type in test_btf.c

1) bpf_load_program_xattr() is absorbing the EBIG error
   which makes testing this case impossible.  It is replaced
   with a direct syscall(__NR_bpf, BPF_PROG_LOAD,...).
2) The test_func_type() is renamed to test_info_raw() to
   prepare for the new line_info test in the next patch.
3) The bpf_obj_get_info_by_fd() testing for func_info
   is refactored to test_get_finfo().  A new
   test_get_linfo() will be added in the next patch
   for testing line_info purpose.
4) The test->func_info_cnt is checked instead of
   a static value "2".
5) Remove unnecessary "\n" in error message.
6) Adding back info_raw_test_num to the cmd arg such
   that a specific test case can be tested, like
   all other existing tests.

7) Fix a bug in handling expected_prog_load_failure.
   A test could pass even if prog_fd != -1 while
   expected_prog_load_failure is true.
8) The min rec_size check should be < 8 instead of < 4.

Fixes: 4798c4ba ("tools/bpf: extends test_btf to test load/retrieve func_type info")
Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Acked-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>