NET: Fix some some more ARP/Ethernet releated configuration

include/nuttx/net/netconfig.h

@@ -89,11 +89,11 @@
 #  ifdef CONFIG_NET_IPv6
 #    error "SLIP is not implemented for IPv6"
 #  endif
-#  define NET_LL_HDRLEN         0
+#  define NET_LL_HDRLEN       0
 #else
 #  define CONFIG_NET_ETHERNET 1
 #  define CONFIG_NET_ARP      1
-#  define NET_LL_HDRLEN         14
+#  define NET_LL_HDRLEN       14
 #endif
 
 /* Layer 3/4 Configuration Options ******************************************/

net/arp/Kconfig

@@ -7,8 +7,8 @@ menu "ARP Configuration"
 
 config NET_ARP
 	bool
-	default y if !NET_SLIP
-	default n if NET_SLIP
+	default y
+	depends on NET_ETHERNET
 	---help---
 		This setting is currently overridden by logic in include/nuttx/net