sd-device: enable SO_PASSCRED again after fork()

When `--daemon` is specified to udevd,

v239:
socket() -> setsockopt(SO_RCVBUFFORCE) -> bind() -> set_nl_address()
  -> setsockopt(SO_PASSCRED) -> fork() -> setsockopt(SO_PASSCRED)

current:
socket() -> setsockopt(SO_RCVBUFFORCE) -> bind() -> set_nl_address()
  -> setsockopt(SO_PASSCRED) -> fork()

So, let's enable SO_PASSCRED again after fork().

src/libsystemd/sd-device/device-monitor.c

@@ -275,11 +275,6 @@ int device_monitor_enable_receiving(sd_device_monitor *m) {
                 return log_debug_errno(r, "sd-device-monitor: Failed to update filter: %m");
 
         if (!m->bound) {
-                /* enable receiving of sender credentials */
-                r = setsockopt_int(m->sock, SOL_SOCKET, SO_PASSCRED, true);
-                if (r < 0)
-                        return log_debug_errno(r, "sd-device-monitor: Failed to set socket option SO_PASSCRED: %m");
-
                 if (bind(m->sock, &m->snl.sa, sizeof(struct sockaddr_nl)) < 0)
                         return log_debug_errno(errno, "sd-device-monitor: Failed to bind monitoring socket: %m");
 
@@ -290,6 +285,11 @@ int device_monitor_enable_receiving(sd_device_monitor *m) {
                         return log_debug_errno(r, "sd-device-monitor: Failed to set address: %m");
         }
 
+        /* enable receiving of sender credentials */
+        r = setsockopt_int(m->sock, SOL_SOCKET, SO_PASSCRED, true);
+        if (r < 0)
+                return log_debug_errno(r, "sd-device-monitor: Failed to set socket option SO_PASSCRED: %m");
+
         return 0;
 }