bpf_load: add map name to load_maps error message

To help when debugging bpf/xdp load issues, have the load_map()
error message include the number and name of the map that
failed.

Signed-off-by: Shannon Nelson <shannon.nelson@oracle.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>