perf report: Fix -D output for user metadata events

perf report: Fix -D output for user metadata events

The PERF_RECORD_USER_ events are synthesized by the tool to assist in
processing the PERF_RECORD_ ones generated by the kernel, the printing
of that information doesn't come with a perf_sample structure, so, when
dumping the event fields using 'perf report -D' there were columns that
end up not being printed.

To tidy up a bit this, fake a perf_sample structure with zeroes to have
the missing columns printed and avoid the occasional surprise with that.

Before:

0 0x45b8 [0x68]: PERF_RECORD_MMAP -1/0: [0xffffffffc12ec000(0x4000) @ 0]: x /lib/modules/4.14.0+/kernel/fs/nls/nls_utf8.ko
0x4620 [0x28]: PERF_RECORD_THREAD_MAP nr: 1 thread: 27820
0x4648 [0x18]: PERF_RECORD_CPU_MAP: 0-3
0 0x4660 [0x28]: PERF_RECORD_COMM: perf:27820/27820
0x4a58 [0x8]: PERF_RECORD_FINISHED_ROUND
447723433020976 0x4688 [0x28]: PERF_RECORD_SAMPLE(IP, 0x4001): 27820/27820: 0xffffffff8f1b6d7a period: 1 addr: 0

After:

  $ perf report -D | grep PERF_RECORD_ | head
  0 0xe8 [0x20]: PERF_RECORD_TIME_CONV: unhandled!
  0 0x108 [0x28]: PERF_RECORD_THREAD_MAP nr: 1 thread: 32555
  0 0x130 [0x18]: PERF_RECORD_CPU_MAP: 0-3
  0 0x148 [0x28]: PERF_RECORD_COMM: perf:32555/32555
  0 0x4e8 [0x8]: PERF_RECORD_FINISHED_ROUND
  448743409421205 0x170 [0x28]: PERF_RECORD_COMM exec: sleep:32555/32555
  448743409431883 0x198 [0x68]: PERF_RECORD_MMAP2 32555/32555: [0x55e11d75a000(0x208000) @ 0 fd:00 3147174 2566255743]: r-xp /usr/bin/sleep
  448743409443873 0x200 [0x70]: PERF_RECORD_MMAP2 32555/32555: [0x7f0ced316000(0x229000) @ 0 fd:00 3151761 2566238119]: r-xp /usr/lib64/ld-2.25.so
  448743409454790 0x270 [0x60]: PERF_RECORD_MMAP2 32555/32555: [0x7ffe84f6d000(0x2000) @ 0 00:00 0 0]: r-xp [vdso]
  448743409479500 0x2d0 [0x28]: PERF_RECORD_SAMPLE(IP, 0x4002): 32555/32555: 0xffffffff8f84c7e7 period: 1 addr: 0
  $

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 9aefcab0de47 ("perf session: Consolidate the dump code")
Link: https://lkml.kernel.org/n/tip-todcu15x0cwgppkh1gi6uhru@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>