selftests: bpf: Fix bind on used port

The bind_perm BPF selftest failed when port 111/tcp was already in use
during the test. To fix this, the test now runs in its own network name
space.

To use unshare, it is necessary to reorder the includes. The style of
the includes is adapted to be consistent with the other prog_tests.

v2: Replace deprecated CHECK macro with ASSERT_OK

Fixes: 8259fdeb ("selftests/bpf: Verify that rebinding to port < 1024 from BPF works")
Signed-off-by: Felix Maurer <fmaurer@redhat.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>
Link: https://lore.kernel.org/bpf/551ee65533bb987a43f93d88eaf2368b416ccd32.1642518457.git.fmaurer@redhat.com

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

 // SPDX-License-Identifier: GPL-2.0
-#include <test_progs.h>
-#include "bind_perm.skel.h"
-
+#define _GNU_SOURCE
+#include <sched.h>
+#include <stdlib.h>
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <sys/capability.h>
 
+#include "test_progs.h"
+#include "bind_perm.skel.h"
+
 static int duration;
 
+static int create_netns(void)
+{
+	if (!ASSERT_OK(unshare(CLONE_NEWNET), "create netns"))
+		return -1;
+
+	return 0;
+}
+
 void try_bind(int family, int port, int expected_errno)
 {
 	struct sockaddr_storage addr = {};
@@ -75,6 +86,9 @@ void test_bind_perm(void)
 	struct bind_perm *skel;
 	int cgroup_fd;
 
+	if (create_netns())
+		return;
+
 	cgroup_fd = test__join_cgroup("/bind_perm");
 	if (CHECK(cgroup_fd < 0, "cg-join", "errno %d", errno))
 		return;