Include btf object id (btf_obj_id) in bpf_map_info so that tools (ex:
bpftools struct_ops dump) know the correct btf from the kernel to look up
type information of struct_ops types.

Since struct_ops types can be defined and registered in a module. The
type information of a struct_ops type are defined in the btf of the
module defining it.  The userspace tools need to know which btf is for
the module defining a struct_ops type.
Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
Link: https://lore.kernel.org/r/20240119225005.668602-7-thinker.li@gmail.comSigned-off-by: Martin KaFai Lau <martin.lau@kernel.org>