network/link: ENODATA from reading IFLA_MASTER when an interface has no master

When an interface leaved from the master interface, then reading
IFLA_MASTER attribute causes ENODATA. When the interface was previously
enslaved to another interface, we need to remove reference to the
interface from the previous master interface.

This is especially important when
```
ip link set dev eth0 nomaster
```
is called.

Fixes a bug introduced by 0d411b7 (v249).
Fixes #37629.

(cherry picked from commit f44b20b7b6c6b0a089a3ec2392ac85e4772e0357)
(cherry picked from commit 2ad46c06069ad4241c94124dd5a3a73da7828048)
(cherry picked from commit c584dfb2051207af017ea1437b3d255023c902f5)
(cherry picked from commit a023d22)

Author: yuwata

src/network/networkd-link.c

@@ -1993,8 +1993,8 @@ static int link_update_master(Link *link, sd_netlink_message *message) {
 
         r = sd_netlink_message_read_u32(message, IFLA_MASTER, (uint32_t*) &master_ifindex);
         if (r == -ENODATA)
-                return 0;
-        if (r < 0)
+                master_ifindex = 0; /* no master interface */
+        else if (r < 0)
                 return log_link_debug_errno(link, r, "rtnl: failed to read master ifindex: %m");
 
         if (master_ifindex == link->ifindex)