MINOR: stats: Report internal errors in the proxies/listeners/servers stats

The stats field ST_F_EINT has been added to report internal errors encountered
per proxy, per listener and per server. It appears in the CLI export and on the
HTML stats page.
diff --git a/include/types/stats.h b/include/types/stats.h
index 4d2a933..bc25a5c 100644
--- a/include/types/stats.h
+++ b/include/types/stats.h
@@ -434,6 +434,7 @@
 	ST_F_CT_MAX,
 	ST_F_RT_MAX,
 	ST_F_TT_MAX,
+	ST_F_EINT,
 
 	/* must always be the last one */
 	ST_F_TOTAL_FIELDS