ctlplane: only mirror valid MTU or MAC values

When creating an interface, its MTU or MAC may still be undetermined
because it hasn't finished its initialization.

For instance, when creating a new port, since commit 05f811a
("iface: make sure to deallocate resources on init failure"),
GR_EVENT_IFACE_ADD is triggered *before* calling iface_set_mtu() which
resolves the mtu field value.

Since the creation of the control plane linux tap interface is triggered
by GR_EVENT_IFACE_ADD, cp_update calls netlink_link_set_mtu(ifindex, 0)
which causes this error log:

    ERR: GROUT: cp_update: netlink_link_set_mtu: Invalid argument

Make sure to only mirror the MTU and MAC address to linux when we have
determined values.

Fixes: 05f811a ("iface: make sure to deallocate resources on init failure")
Signed-off-by: Robin Jarry <rjarry@redhat.com>
Reviewed-by: Christophe Fontaine <cfontain@redhat.com>

Author: rjarry

modules/infra/control/ctlplane.c

@@ -388,12 +388,23 @@ static void cp_update(struct iface *iface) {
 			    strerror(errno));
 	}
 
-	if (netlink_link_set_mtu(iface->cp_id, iface->mtu) < 0)
-		LOG(ERR, "netlink_link_set_mtu: %s", strerror(errno));
+	if (iface->mtu != 0) {
+		if (netlink_link_set_mtu(iface->cp_id, iface->mtu) < 0)
+			LOG(ERR,
+			    "netlink_link_set_mtu(%s, %u): %s",
+			    iface->name,
+			    iface->mtu,
+			    strerror(errno));
+	}
 
-	iface_get_eth_addr(iface, &mac);
-	if (netlink_link_set_mac(iface->cp_id, &mac) < 0)
-		LOG(ERR, "netlink_link_set_mac: %s", strerror(errno));
+	if (iface_get_eth_addr(iface, &mac) == 0) {
+		if (netlink_link_set_mac(iface->cp_id, &mac) < 0)
+			LOG(ERR,
+			    "netlink_link_set_mac(%s, " ETH_F "): %s",
+			    iface->name,
+			    &mac,
+			    strerror(errno));
+	}
 }
 
 static void iface_event(uint32_t event, const void *obj) {