Add FEATURE() macro, plus code to display features at startup time,

and generate DHCP options to indicate features to DHCP server (and to
PXE NBPs).

src/net/tcp/iscsi.c

@@ -32,6 +32,7 @@
 #include <gpxe/uaccess.h>
 #include <gpxe/tcpip.h>
 #include <gpxe/dhcp.h>
+#include <gpxe/features.h>
 #include <gpxe/iscsi.h>
 
 /** @file
@@ -40,6 +41,8 @@
  *
  */
 
+FEATURE ( "iSCSI", DHCP_EB_FEATURE_ISCSI );
+
 /** iSCSI initiator name (explicitly specified) */
 static char *iscsi_explicit_initiator_iqn;