Allowed zero-cost enforced ordering of features in startup banner

list.

Added FEATURE() macros to most relevant (non-driver) files.

src/net/udp/dns.c

@@ -31,6 +31,7 @@
 #include <gpxe/retry.h>
 #include <gpxe/tcpip.h>
 #include <gpxe/dhcp.h>
+#include <gpxe/features.h>
 #include <gpxe/dns.h>
 
 /** @file
@@ -39,6 +40,8 @@
  *
  */
 
+FEATURE ( FEATURE_PROTOCOL, "DNS", DHCP_EB_FEATURE_DNS, 1 );
+
 /** The DNS server */
 static struct sockaddr_tcpip nameserver = {
 	.st_port = htons ( DNS_PORT ),