nntp: consistently use 501 for unsupported LIST

This is required by RFC 3977, section 3.2.1

1 files changed, 2 insertions, 2 deletions

diff --git a/lib/PublicInbox/NNTP.pm b/lib/PublicInbox/NNTP.pm
index c2f97177..dd033e89 100644
--- a/lib/PublicInbox/NNTP.pm
+++ b/lib/PublicInbox/NNTP.pm
@@ -123,14 +123,14 @@ sub list_newsgroups ($;$) {
         }
 }
 
-# LIST SUBSCRIPTIONS not supported
+# LIST SUBSCRIPTIONS, DISTRIB.PATS are not supported
 sub cmd_list ($;$$) {
         my ($self, @args) = @_;
         if (scalar @args) {
                 my $arg = shift @args;
                 $arg =~ tr/A-Z./a-z_/;
                 $arg = "list_$arg";
-                return '503 function not performed' if $DISABLED{$arg};
+                return r501 if $DISABLED{$arg};
 
                 $arg = eval {
                         no strict 'refs';