[AX25] Introduce ax25_type_trans

Replacing the open coded equivalents and making ax25 look more like
a linux network protocol, i.e. more similar to inet.

Signed-off-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ax25/ax25_ds_subr.c b/net/ax25/ax25_ds_subr.c
index 10ffd2b..1d4ab64 100644
--- a/net/ax25/ax25_ds_subr.c
+++ b/net/ax25/ax25_ds_subr.c
@@ -143,8 +143,7 @@
 	*p++ = cmd;
 	*p++ = param;
 
-	skb->dev      = ax25_dev->dev;
-	skb->protocol = htons(ETH_P_AX25);
+	skb->protocol = ax25_type_trans(skb, ax25_dev->dev);
 
 	dev_queue_xmit(skb);
 }