net: Move ARP out of net.c

Separate this functionality out of the net.c behemoth

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Acked-by: Simon Glass <sjg@chromium.org>
Acked-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/net/Makefile b/net/Makefile
index b350bfc..0916a56 100644
--- a/net/Makefile
+++ b/net/Makefile
@@ -27,6 +27,7 @@
 
 LIB	= $(obj)libnet.o
 
+COBJS-$(CONFIG_CMD_NET)  += arp.o
 COBJS-$(CONFIG_CMD_NET)  += bootp.o
 COBJS-$(CONFIG_CMD_CDP)  += cdp.o
 COBJS-$(CONFIG_CMD_DNS)  += dns.o