network: increase receive buffer size for device monitor

If networkd creates huge amount of netdevs, then the buffer of device
monitor becomes easily flowed.

Hopefully fixes #16865.

src/network/networkd-manager.c

@@ -270,6 +270,10 @@ static int manager_connect_udev(Manager *m) {
         if (r < 0)
                 return log_error_errno(r, "Failed to initialize device monitor: %m");
 
+        r = sd_device_monitor_set_receive_buffer_size(m->device_monitor, RCVBUF_SIZE);
+        if (r < 0)
+                log_warning_errno(r, "Failed to increase buffer size for device monitor, ignoring: %m");
+
         r = sd_device_monitor_filter_add_match_subsystem_devtype(m->device_monitor, "net", NULL);
         if (r < 0)
                 return log_error_errno(r, "Could not add device monitor filter: %m");