samples/bpf: fix bpf loader

llvm can emit relocations into sections other than program code
(like debug info sections). Ignore them during parsing of elf file

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>