Currently we'll only print metric headers for metric leader in
aggregration mode. This will make `perf iostat` header not shown
since it'll aggregrated globally but don't have metric events:

  root@ubuntu204:/home/yang/linux/tools/perf# ./perf stat --iostat --timeout 1000
   Performance counter stats for 'system wide':
      port
  0000:00                    0                    0                    0                    0
  0000:80                    0                    0                    0                    0
  [...]

Fix this by excluding the iostat in the check of printing metric
headers. Then we can see the headers:

  root@ubuntu204:/home/yang/linux/tools/perf# ./perf stat --iostat --timeout 1000
   Performance counter stats for 'system wide':
      port             Inbound Read(MB)    Inbound Write(MB)    Outbound Read(MB)   Outbound Write(MB)
  0000:00                    0                    0                    0                    0
  0000:80                    0                    0                    0                    0
  [...]

Fixes: 193a9e30 ("perf stat: Don't display metric header for non-leader uncore events")
Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jonathan Cameron <jonathan.cameron@huawei.com>
Cc: Junhao He <hejunhao3@huawei.com>
Cc: linuxarm@huawei.com
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>
Cc: Zeng Tao <prime.zeng@hisilicon.com>
Link: https://lore.kernel.org/r/20240802065800.48774-1-yangyicong@huawei.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>