[MEDIUM] acl: set types on all currently known ACL verbs

All currently known ACL verbs have been assigned a type which makes
it possible to detect inconsistencies, such as response values used
in request rules.
diff --git a/src/backend.c b/src/backend.c
index ddedfd9..7fbc720 100644
--- a/src/backend.c
+++ b/src/backend.c
@@ -2138,7 +2138,7 @@
 
 /* Note: must not be declared <const> as its list will be overwritten */
 static struct acl_kw_list acl_kws = {{ },{
-	{ "nbsrv",   acl_parse_int,   acl_fetch_nbsrv,    acl_match_int },
+	{ "nbsrv",   acl_parse_int,   acl_fetch_nbsrv,    acl_match_int, ACL_USE_NOTHING },
 	{ NULL, NULL, NULL, NULL },
 }};