bpf: implement decoding of BPF_TASK_FD_QUERY command

bpf: implement decoding of BPF_TASK_FD_QUERY command

BPF_TASK_FD_QUERY command was introduced by Linux commit
v4.18-rc1~114^2~148^2~1^2~5.

* bpf_attr.h (struct BPF_TASK_FD_QUERY_struct): New type.
(BPF_TASK_FD_QUERY_struct_size,
expected_BPF_TASK_FD_QUERY_struct_size): New macros.
* bpf.c: Include "xlat/bpf_task_fd_type.h".
(BEGIN_BPF_CMD_DECODER(BPF_TASK_FD_QUERY)): New bpf command decoder.
(SYS_FUNC(bpf)) <bpf_cmd_decoders[]>: Add
BPF_CMD_ENTRY(BPF_TASK_FD_QUERY).
* xlat/bpf_task_fd_type.in: New file.
* tests/bpf.c (union bpf_attr_data): Add
BPF_ATTR_DATA_FIELD(BPF_TASK_FD_QUERY).
(BPF_TASK_FD_QUERY_checks): New checks array.
(main) <checks>: Add CHK(BPF_TASK_FD_QUERY).