selftests: rtnetlink: add addresses with fixed life time

This exercises kernel code path that deal with addresses that have
a limited lifetime.

Without previous fix, this triggers following crash on net-next:
 BUG: KASAN: null-ptr-deref in check_lifetime+0x403/0x670
 Read of size 8 at addr 0000000000000010 by task kworker [..]
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

tools/testing/selftests/net/rtnetlink.sh

@@ -249,6 +249,26 @@ kci_test_route_get()
 	echo "PASS: route get"
 }
 
+kci_test_addrlft()
+{
+	for i in $(seq 10 100) ;do
+		lft=$(((RANDOM%3) + 1))
+		ip addr add 10.23.11.$i/32 dev "$devdummy" preferred_lft $lft valid_lft $((lft+1))
+		check_err $?
+	done
+
+	sleep 5
+
+	ip addr show dev "$devdummy" | grep "10.23.11."
+	if [ $? -eq 0 ]; then
+		echo "FAIL: preferred_lft addresses remaining"
+		check_err 1
+		return
+	fi
+
+	echo "PASS: preferred_lft addresses have expired"
+}
+
 kci_test_addrlabel()
 {
 	ret=0
@@ -1140,6 +1160,7 @@ kci_test_rtnl()
 
 	kci_test_polrouting
 	kci_test_route_get
+	kci_test_addrlft
 	kci_test_tc
 	kci_test_gre
 	kci_test_gretap