tun tests: Test renaming and destroying a tun interface in a vnet jail

There was a problem destroying renamed tun interfaces in vnet jails. This was
fixed in r344794. Test the previously failing scenario.

PR:		235704
MFC after:	2 weeks

tests/sys/net/Makefile

@@ -7,6 +7,7 @@ BINDIR=		${TESTSDIR}
 
 ATF_TESTS_SH+=	if_lagg_test
 ATF_TESTS_SH+=	if_clone_test
+ATF_TESTS_SH+=	if_tun_test
 
 # The tests are written to be run in parallel, but doing so leads to random
 # panics.  I think it's because the kernel's list of interfaces isn't properly

tests/sys/net/if_tun_test.sh

@@ -0,0 +1,30 @@
+# $FreeBSD$
+
+. $(atf_get_srcdir)/../common/vnet.subr
+
+atf_test_case "235704" "cleanup"
+235704_head()
+{
+	atf_set descr "Test PR #235704"
+	atf_set require.user root
+}
+
+235704_body()
+{
+	vnet_init
+	vnet_mkjail one
+
+	tun=$(jexec one ifconfig tun create)
+	jexec one ifconfig ${tun} name foo
+	atf_check -s exit:0 jexec one ifconfig foo destroy
+}
+
+235704_cleanup()
+{
+	vnet_cleanup
+}
+
+atf_init_test_cases()
+{
+	atf_add_test_case "235704"
+}