libbpf: Cleanup temp FDs when intermediate sys_bpf fails.

Fix loader program to close temporary FDs when intermediate
sys_bpf command fails.

Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20210514003623.28033-16-alexei.starovoitov@gmail.com

src/bpf_gen_internal.h

@@ -15,6 +15,7 @@ struct bpf_gen {
 	void *data_cur;
 	void *insn_start;
 	void *insn_cur;
+	ssize_t cleanup_label;
 	__u32 nr_progs;
 	__u32 nr_maps;
 	int log_level;