snap: use const for descriptor

Protocols should be able to use constant value for the descriptor.
Minor whitespace cleanup as well

Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/psnap.h b/include/net/psnap.h
index b2e01cc..fe456c2 100644
--- a/include/net/psnap.h
+++ b/include/net/psnap.h
@@ -1,7 +1,11 @@
 #ifndef _NET_PSNAP_H
 #define _NET_PSNAP_H
 
-extern struct datalink_proto *register_snap_client(unsigned char *desc, int (*rcvfunc)(struct sk_buff *, struct net_device *, struct packet_type *, struct net_device *orig_dev));
+extern struct datalink_proto *
+register_snap_client(const unsigned char *desc,
+		     int (*rcvfunc)(struct sk_buff *, struct net_device *,
+				    struct packet_type *,
+				    struct net_device *orig_dev));
 extern void unregister_snap_client(struct datalink_proto *proto);
 
 #endif