Fixed change prerequisites for <net/if_arp.h>:

- don't declare `struct arpcom' except in the kernel, so that there is no
  dependency on <net/if.h> except in the kernel.  This may break something
  else.
- spell ETHER_ADDR_LEN as 6 again, so that there is no dependency on
  <net/ethernet.h> even in the kernel.

sys/net/if_arp.h

@@ -31,7 +31,7 @@
  * SUCH DAMAGE.
  *
  *	@(#)if_arp.h	8.1 (Berkeley) 6/10/93
- * $Id: if_arp.h,v 1.8 1997/02/22 09:40:59 peter Exp $
+ * $Id: if_arp.h,v 1.9 1998/01/08 23:41:18 eivind Exp $
  */
 
 #ifndef _NET_IF_ARP_H_
@@ -88,6 +88,7 @@ struct arpreq {
 #define	ATF_PUBL	0x08	/* publish entry (respond for other host) */
 #define	ATF_USETRAILERS	0x10	/* has requested trailers */
 
+#ifdef KERNEL
 /*
  * Structure shared between the ethernet driver modules and
  * the address resolution code.  For example, each ec_softc or il_softc
@@ -98,12 +99,11 @@ struct	arpcom {
 	 * The ifnet struct _must_ be at the head of this structure.
 	 */
 	struct 	ifnet ac_if;		/* network-visible interface */
-	u_char	ac_enaddr[ETHER_ADDR_LEN];		/* ethernet hardware address */
+	u_char	ac_enaddr[6];		/* ethernet hardware address */
 	int	ac_multicnt;		/* length of ac_multiaddrs list */
 };
 
-#ifdef KERNEL
-extern u_char	etherbroadcastaddr[ETHER_ADDR_LEN];
+extern u_char	etherbroadcastaddr[6];
 #endif
 
 #endif /* !_NET_IF_ARP_H_ */