net: Use env callbacks for net variables

Instead of checking for changes to the env each time we enter the
net_loop, use the env callbacks to update the values of the variables.
Don't update the variables when the source was programmatic, since the
variables were the source of the new value.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

include/env_callback.h

@@ -37,6 +37,26 @@
 #define ENV_DOT_ESCAPE
 #endif
 
+#ifdef CONFIG_CMD_DNS
+#define DNS_CALLBACK "dnsip:dnsip,"
+#else
+#define DNS_CALLBACK
+#endif
+
+#ifdef CONFIG_NET
+#define NET_CALLBACKS \
+	"bootfile:bootfile," \
+	"ipaddr:ipaddr," \
+	"gatewayip:gatewayip," \
+	"netmask:netmask," \
+	"serverip:serverip," \
+	"nvlan:nvlan," \
+	"vlan:vlan," \
+	DNS_CALLBACK
+#else
+#define NET_CALLBACKS
+#endif
+
 /*
  * This list of callback bindings is static, but may be overridden by defining
  * a new association in the ".callbacks" environment variable.
@@ -44,7 +64,7 @@
 #define ENV_CALLBACK_LIST_STATIC ENV_DOT_ESCAPE ENV_CALLBACK_VAR ":callbacks," \
 	ENV_DOT_ESCAPE ENV_FLAGS_VAR ":flags," \
 	"baudrate:baudrate," \
-	"bootfile:bootfile," \
+	NET_CALLBACKS \
 	"loadaddr:loadaddr," \
 	SILENT_CALLBACK \
 	SPLASHIMAGE_CALLBACK \