samples/bpf: fix compilation failure

following commit:
commit d58e468b11 ("flow_dissector: implements flow dissector BPF hook")
added struct bpf_flow_keys which conflicts with the struct with
same name in sockex2_kern.c and sockex3_kern.c

similar to commit:
commit 534e0e52bc ("samples/bpf: fix a compilation failure")
we tried the rename it "flow_keys" but it also conflicted with struct
having same name in include/net/flow_dissector.h. Hence renaming the
struct to "flow_key_record". Also, this commit doesn't fix the
compilation error completely because the similar struct is present in
sockex3_kern.c. Hence renaming it in both files sockex3_user.c and
sockex3_kern.c

Signed-off-by: Prashant Bhole <bhole_prashant_q7@lab.ntt.co.jp>
Acked-by: Song Liu <songliubraving@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 flow_keys {
+struct flow_key_record {
 	__be32 src;
 	__be32 dst;
 	union {
@@ -64,7 +64,7 @@ int main(int argc, char **argv)
 	(void) f;
 
 	for (i = 0; i < 5; i++) {
-		struct flow_keys key = {}, next_key;
+		struct flow_key_record key = {}, next_key;
 		struct pair value;
 
 		sleep(1);