bpf: move handling of the saved state to BPF_OBJ_GET_INFO_BY_FD decoder

bpf: move handling of the saved state to BPF_OBJ_GET_INFO_BY_FD decoder

As it is needed for proper info_len printing on exiting.

* bpf.c (print_bpf_obj_info_fn): Change return type to void, add "saved"
argument.
(struct obj_get_info_saved): New type definition.
(print_bpf_map_info, print_bpf_prog_info): Change return type to void,
add "saved" argument, do not handle private tcb data allocation and
obtainment.
(print_bpf_obj_info_addr): Change return type to void, add tcb argument,
print the address only on exiting.
(print_bpf_obj_info): Change return type to void, add "saved" argument.
(BEGIN_BPF_CMD_DECODER(BPF_OBJ_GET_INFO_BY_FD)): Handle private data
allocation/saving/restoring, use it for storing/printing info_len field.

Co-Authored-by: Dmitry V. Levin <ldv@altlinux.org>