net: pull CONFIG checks out of source and into makefile

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>
diff --git a/net/Makefile b/net/Makefile
index ff87d87..4f819dd 100644
--- a/net/Makefile
+++ b/net/Makefile
@@ -27,14 +27,14 @@
 
 LIB	= $(obj)libnet.a
 
-COBJS-y += bootp.o
+COBJS-$(CONFIG_CMD_NET)  += bootp.o
 COBJS-$(CONFIG_CMD_DNS)  += dns.o
-COBJS-y += eth.o
-COBJS-y += net.o
-COBJS-y += nfs.o
-COBJS-y += rarp.o
+COBJS-$(CONFIG_CMD_NET)  += eth.o
+COBJS-$(CONFIG_CMD_NET)  += net.o
+COBJS-$(CONFIG_CMD_NFS)  += nfs.o
+COBJS-$(CONFIG_CMD_NET)  += rarp.o
 COBJS-$(CONFIG_CMD_SNTP) += sntp.o
-COBJS-y += tftp.o
+COBJS-$(CONFIG_CMD_NET)  += tftp.o
 
 COBJS	:= $(COBJS-y)
 SRCS	:= $(COBJS:.o=.c)