devices: propagate the hop limit from an IPv6 RA to the kernel config

If we set accept_ra_defrtr=0 then the kernel will ignore the "hop
limit" too. So parse it out of the RA and set it manually.

src/devices/nm-device.c

@@ -430,6 +430,7 @@ static const char *ip6_properties_to_save[] = {
 	"accept_ra_pinfo",
 	"accept_ra_rtr_pref",
 	"disable_ipv6",
+	"hop_limit",
 	"use_tempaddr",
 };
 
@@ -3479,6 +3480,13 @@ rdisc_config_changed (NMRDisc *rdisc, NMRDiscConfigMap changed, NMDevice *device
 		}
 	}
 
+	if (changed & NM_RDISC_CONFIG_HOP_LIMIT) {
+		char val[16];
+
+		g_snprintf (val, sizeof (val), "%d", rdisc->hop_limit);
+		nm_device_ipv6_sysctl_set (device, "hop_limit", val);
+	}
+
 	nm_device_activate_schedule_ip6_config_result (device);
 }