selftests/bpf: Allow auto port binding for bpf nf

Allow auto port binding for bpf nf test to avoid binding conflict.

./test_progs -a bpf_nf
24/1    bpf_nf/xdp-ct:OK
24/2    bpf_nf/tc-bpf-ct:OK
24/3    bpf_nf/alloc_release:OK
24/4    bpf_nf/insert_insert:OK
24/5    bpf_nf/lookup_insert:OK
24/6    bpf_nf/set_timeout_after_insert:OK
24/7    bpf_nf/set_status_after_insert:OK
24/8    bpf_nf/change_timeout_after_alloc:OK
24/9    bpf_nf/change_status_after_alloc:OK
24/10   bpf_nf/write_not_allowlisted_field:OK
24      bpf_nf:OK
Summary: 1/10 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Jiayuan Chen <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: mrpre

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

@@ -72,11 +72,14 @@ static void test_bpf_nf_ct(int mode)
 	if (!ASSERT_OK(system(cmd), cmd))
 		goto end;
 
-	srv_port = (mode == TEST_XDP) ? 5005 : 5006;
-	srv_fd = start_server(AF_INET, SOCK_STREAM, "127.0.0.1", srv_port, TIMEOUT_MS);
+	srv_fd = start_server(AF_INET, SOCK_STREAM, "127.0.0.1", 0, TIMEOUT_MS);
 	if (!ASSERT_GE(srv_fd, 0, "start_server"))
 		goto end;
 
+	srv_port = get_socket_local_port(srv_fd);
+	if (!ASSERT_GE(srv_port, 0, "get_sock_local_port"))
+		goto end;
+
 	client_fd = connect_to_server(srv_fd);
 	if (!ASSERT_GE(client_fd, 0, "connect_to_server"))
 		goto end;
@@ -91,7 +94,7 @@ static void test_bpf_nf_ct(int mode)
 	skel->bss->saddr = peer_addr.sin_addr.s_addr;
 	skel->bss->sport = peer_addr.sin_port;
 	skel->bss->daddr = peer_addr.sin_addr.s_addr;
-	skel->bss->dport = htons(srv_port);
+	skel->bss->dport = srv_port;
 
 	if (mode == TEST_XDP)
 		prog_fd = bpf_program__fd(skel->progs.nf_xdp_ct_test);