can: fix sparse warning in af_can.c

Put can_rx_alldev_list into the af_can header to fix the following
sparse warning: net/can/af_can.c:80:22: warning: symbol
'can_rx_alldev_list' was not declared. Should it be static?
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

net/can/af_can.h

@@ -104,6 +104,9 @@ struct s_pstats {
 	unsigned long rcv_entries_max;
 };
 
+/* receive filters subscribed for 'all' CAN devices */
+extern struct dev_rcv_lists can_rx_alldev_list;
+
 /* function prototypes for the CAN networklayer procfs (proc.c) */
 extern void can_init_proc(void);
 extern void can_remove_proc(void);

net/can/proc.c

@@ -83,9 +83,6 @@ static const char rx_list_name[][8] = {
 	[RX_EFF] = "rx_eff",
 };
 
-/* receive filters subscribed for 'all' CAN devices */
-extern struct dev_rcv_lists can_rx_alldev_list;
-
 /*
  * af_can statistics stuff
  */