MINOR: stats: emit dses

This is the number of denied sessions, blocked by "tcp-request session reject".
diff --git a/include/proto/dumpstats.h b/include/proto/dumpstats.h
index 633beca..db60bab 100644
--- a/include/proto/dumpstats.h
+++ b/include/proto/dumpstats.h
@@ -205,6 +205,7 @@
 	ST_F_CONN_TOT,
 	ST_F_INTERCEPTED,
 	ST_F_DCON,
+	ST_F_DSES,
 
 	/* must always be the last one */
 	ST_F_TOTAL_FIELDS