Enable KeepAddrOnDown for ipv6 addresses

This enables the keep_addr_on_down sysctl parameter for
IPV6 addresses configured via the ConfigureIface function.

This prevents IPAM confiuration to be lost when users need
to refresh the link state of an interface that has IPV6 addresses.

Signed-off-by: Marcelo Guerrero <marguerr@redhat.com>

pkg/ipam/ipam_linux_test.go

@@ -201,6 +201,49 @@ var _ = Describe("ConfigureIface", func() {
 		Expect(err).NotTo(HaveOccurred())
 	})
 
+	It("keeps IPV6 addresses after the interface is brought down", func() {
+		err := originalNS.Do(func(ns.NetNS) error {
+			defer GinkgoRecover()
+
+			By("Configuring the interface")
+
+			err := ConfigureIface(LINK_NAME, result)
+			Expect(err).NotTo(HaveOccurred())
+
+			By("Verifying the IPV6 address is present")
+
+			link, err := netlinksafe.LinkByName(LINK_NAME)
+			Expect(err).NotTo(HaveOccurred())
+			Expect(link.Attrs().Name).To(Equal(LINK_NAME))
+
+			v6addrs, err := netlinksafe.AddrList(link, syscall.AF_INET6)
+			Expect(err).NotTo(HaveOccurred())
+			Expect(v6addrs).To(HaveLen(2))
+
+			var found bool
+			for _, a := range v6addrs {
+				if ipNetEqual(a.IPNet, ipv6) {
+					found = true
+					break
+				}
+			}
+			Expect(found).To(BeTrue())
+
+			By("Bringing the interface down")
+			err = netlink.LinkSetDown(link)
+			Expect(err).NotTo(HaveOccurred())
+
+			By("Verifying the IPV6 address is still present")
+			v6addrs, err = netlinksafe.AddrList(link, syscall.AF_INET6)
+			Expect(err).NotTo(HaveOccurred())
+			Expect(v6addrs).To(HaveLen(1))
+			Expect(ipNetEqual(v6addrs[0].IPNet, ipv6)).To(BeTrue())
+
+			return nil
+		})
+		Expect(err).NotTo(HaveOccurred())
+	})
+
 	It("configures a link with routes using address gateways", func() {
 		result.Routes[0].GW = nil
 		result.Routes[1].GW = nil