[settings] Explicitly separate the concept of a completed fetched setting

The fetch_setting() family of functions may currently modify the
definition of the specified setting (e.g. to add missing type
information).  Clean up this interface by requiring callers to provide
an explicit buffer to contain the completed definition of the fetched
setting, if required.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/usr/nslookup.c

@@ -71,7 +71,7 @@ static void nslookup_close ( struct nslookup *nslookup, int rc ) {
 static void nslookup_resolv_done ( struct nslookup *nslookup,
 				   struct sockaddr *sa ) {
 	struct sockaddr_in *sin;
-	struct setting_type *default_type;
+	const struct setting_type *default_type;
 	struct settings *settings;
 	struct setting setting;
 	void *data;