Detect windows hosts to add specific workarounds.

src/pluto/demux.h

@@ -61,6 +61,7 @@ struct msg_digest {
 	notification_t note;        /* reason for failure */
 	bool dpd;                   /* peer supports RFC 3706 DPD */
 	bool openpgp;               /* peer supports OpenPGP certificates */
+	bool ms_nt5;                /* peer is a windows 2000+ host */
 
 #   define PAYLIMIT 40
 	struct payload_digest

src/pluto/vendor.c

@@ -382,6 +382,12 @@ static void handle_known_vendorid (struct msg_digest *md, const char *vidstr,
 		vid_useful = TRUE;
 		break;
 
+	/* Remote side is a Windows 2000+ host */
+	case VID_MS_NT5:
+		md->ms_nt5 = TRUE;
+		vid_useful = TRUE;
+		break;
+
 	/*
 	 * Use most recent supported NAT-Traversal method and ignore the
 	 * other ones (implementations will send all supported methods but