can: unify identifiers to ensure unique include processing

Armin pointed me to the fact that the identifier which is used to ensure the
unique include processing in lunux/include/uapi/linux/can.h is CAN_H.
This clashed with his own source as includes from libraries and APIs should
use an underscore '_' at the identifier start.

This patch fixes the protection identifiers in all CAN relavant includes.

Reported-by: Armin Burchardt <armin@uni-bremen.de>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
diff --git a/include/linux/can/skb.h b/include/linux/can/skb.h
index f9bbbb4..cc00d15 100644
--- a/include/linux/can/skb.h
+++ b/include/linux/can/skb.h
@@ -7,8 +7,8 @@
  *
  */
 
-#ifndef CAN_SKB_H
-#define CAN_SKB_H
+#ifndef _CAN_SKB_H
+#define _CAN_SKB_H
 
 #include <linux/types.h>
 #include <linux/skbuff.h>
@@ -80,4 +80,4 @@
 	return skb;
 }
 
-#endif /* CAN_SKB_H */
+#endif /* !_CAN_SKB_H */