samples/bpf: fix bpf_perf_event_output prototype

The commit 555c8a8623a3 ("bpf: avoid stack copy and use skb ctx for event output")
started using 20 of initially reserved upper 32-bits of 'flags' argument
in bpf_perf_event_output(). Adjust corresponding prototype in samples/bpf/bpf_helpers.h

Signed-off-by: Adam Barth <arb@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

samples/bpf/bpf_helpers.h

@@ -37,7 +37,9 @@ static int (*bpf_clone_redirect)(void *ctx, int ifindex, int flags) =
 	(void *) BPF_FUNC_clone_redirect;
 static int (*bpf_redirect)(int ifindex, int flags) =
 	(void *) BPF_FUNC_redirect;
-static int (*bpf_perf_event_output)(void *ctx, void *map, int index, void *data, int size) =
+static int (*bpf_perf_event_output)(void *ctx, void *map,
+				    unsigned long long flags, void *data,
+				    int size) =
 	(void *) BPF_FUNC_perf_event_output;
 static int (*bpf_get_stackid)(void *ctx, void *map, int flags) =
 	(void *) BPF_FUNC_get_stackid;