busybox: fix arping applet building on musl

musl-libc is more strict about missing includes.

Signed-off-by: Florian Fainelli <florian@openwrt.org>

SVN-Revision: 34311

package/busybox/patches/998-arping_missing_includes.patch

@@ -0,0 +1,12 @@
+diff -urN busybox-1.19.4/networking/arping.c busybox-1.19.4.new/networking/arping.c
+--- busybox-1.19.4/networking/arping.c	2012-02-04 20:24:55.000000000 +0100
++++ busybox-1.19.4.new/networking/arping.c	2012-11-23 17:22:13.753252564 +0100
+@@ -24,6 +24,8 @@
+ 
+ #include <arpa/inet.h>
+ #include <net/if.h>
++#include <net/if_arp.h>
++#include <netinet/if_ether.h>
+ #include <netinet/ether.h>
+ #include <netpacket/packet.h>
+