bpf.2: Fix bug in example

mtk: checked also against examples in samples/bpf
in kernel source to confirm.

Signed-off-by: Oded Elisha <oded123456@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/bpf.2

@@ -988,7 +988,7 @@ main(int argc, char **argv)
     };
 
     prog_fd = bpf_prog_load(BPF_PROG_TYPE_SOCKET_FILTER, prog,
-                            sizeof(prog), "GPL");
+                            sizeof(prog) / sizeof(prog[0]), "GPL");
 
     sock = open_raw_sock("lo");