selftests/bpf: fix a compilation error

I hit the following compilation error with gcc 4.8.5.

  prog_tests/flow_dissector.c: In function ‘test_flow_dissector’:
  prog_tests/flow_dissector.c:155:2: error: ‘for’ loop initial declarations are only allowed in C99 mode
    for (int i = 0; i < ARRAY_SIZE(tests); i++) {
    ^
  prog_tests/flow_dissector.c:155:2: note: use option -std=c99 or -std=gnu99 to compile your code

Let us fix the issue by avoiding this particular c99 feature.

Fixes: a5cb3346 ("selftests/bpf: make flow dissector tests more extensible")
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/testing/selftests/bpf/prog_tests/flow_dissector.c

@@ -143,7 +143,7 @@ struct test tests[] = {
 void test_flow_dissector(void)
 {
 	struct bpf_object *obj;
-	int err, prog_fd;
+	int i, err, prog_fd;
 
 	err = bpf_flow_load(&obj, "./bpf_flow.o", "flow_dissector",
 			    "jmp_table", &prog_fd);
@@ -152,7 +152,7 @@ void test_flow_dissector(void)
 		return;
 	}
 
-	for (int i = 0; i < ARRAY_SIZE(tests); i++) {
+	for (i = 0; i < ARRAY_SIZE(tests); i++) {
 		struct bpf_flow_keys flow_keys;
 		struct bpf_prog_test_run_attr tattr = {
 			.prog_fd = prog_fd,