samples/bpf: fix a compilation failure

samples/bpf build failed with the following errors:

  $ make samples/bpf/
  ...
  HOSTCC  samples/bpf/sockex3_user.o
  /data/users/yhs/work/net-next/samples/bpf/sockex3_user.c:16:8: error: redefinition of ‘struct bpf_flow_keys’
   struct bpf_flow_keys {
          ^
  In file included from /data/users/yhs/work/net-next/samples/bpf/sockex3_user.c:4:0:
  ./usr/include/linux/bpf.h:2338:9: note: originally defined here
    struct bpf_flow_keys *flow_keys;
           ^
  make[3]: *** [samples/bpf/sockex3_user.o] Error 1

Commit d58e468 ("flow_dissector: implements flow dissector BPF hook")
introduced struct bpf_flow_keys in include/uapi/linux/bpf.h and hence
caused the naming conflict with samples/bpf/sockex3_user.c.

The fix is to rename struct bpf_flow_keys in samples/bpf/sockex3_user.c
to flow_keys to avoid the conflict.

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

samples/bpf/sockex3_user.c

@@ -13,7 +13,7 @@
 #define PARSE_IP_PROG_FD (prog_fd[0])
 #define PROG_ARRAY_FD (map_fd[0])
 
-struct bpf_flow_keys {
+struct flow_keys {
 	__be32 src;
 	__be32 dst;
 	union {
@@ -64,7 +64,7 @@ int main(int argc, char **argv)
 	(void) f;
 
 	for (i = 0; i < 5; i++) {
-		struct bpf_flow_keys key = {}, next_key;
+		struct flow_keys key = {}, next_key;
 		struct pair value;
 
 		sleep(1);