varlink: say which socket failed to bind in log message

Makes it a lot easier to debug failures

src/network/networkd-manager-varlink.c

@@ -324,7 +324,7 @@ int manager_connect_varlink(Manager *m, int fd) {
         else
                 r = sd_varlink_server_listen_fd(s, fd);
         if (r < 0)
-                return log_error_errno(r, "Failed to bind to varlink socket: %m");
+                return log_error_errno(r, "Failed to bind to varlink socket '/run/systemd/netif/io.systemd.Network': %m");
 
         TAKE_FD(fd_close);