Kconfig: cmd: Make networking command dependent on NET

Enable networking command only when NET is enabled.
And remove selecting NET for CMD_NET

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/include/env_callback.h b/include/env_callback.h
index 5c4a30c..48da32a 100644
--- a/include/env_callback.h
+++ b/include/env_callback.h
@@ -45,7 +45,7 @@
 #define DNS_CALLBACK
 #endif
 
-#ifdef CONFIG_NET
+#ifdef CONFIG_CMD_NET
 #define NET_CALLBACKS \
 	"bootfile:bootfile," \
 	"ipaddr:ipaddr," \