perf test BPF: Fixup BPF test using epoll_pwait syscall function probe

Since e145242e ("syscalls/core, syscalls/x86: Clean up syscall stub
naming convention") changed the main syscall function for 'epoll_pwait'
to something other than the expected 'SyS_epoll_pwait the' 'perf test
BPF' entries started failing, fix it by using something called from the
main syscall function instead, 'epoll_wait', which should keep this test
working in older kernels too.

Before:

  # perf test BPF
  40: BPF filter                           :
  40.1: Basic BPF filtering                : FAILED!
  40.2: BPF pinning                        : Skip
  40.3: BPF prologue generation            : Skip
  40.4: BPF relocation checker             : Skip

If we use -v for that test we see the problem:

    Probe point 'SyS_epoll_pwait' not found.

After:

  # perf test BPF
  40: BPF filter                           :
  40.1: Basic BPF filtering                : Ok
  40.2: BPF pinning                        : Ok
  40.3: BPF prologue generation            : Ok
  40.4: BPF relocation checker             : Ok
  #

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Dominik Brodowski <linux@dominikbrodowski.net>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: https://lkml.kernel.org/r/tip-y24nmn70cs2am8jh4i344dng@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/bpf-script-example.c

@@ -31,7 +31,7 @@ struct bpf_map_def SEC("maps") flip_table = {
 	.max_entries = 1,
 };
 
-SEC("func=SyS_epoll_pwait")
+SEC("func=do_epoll_wait")
 int bpf_func__SyS_epoll_pwait(void *ctx)
 {
 	int ind =0;