snomasks: make +s a parametric snomask mode with the standard category letters (acdfgjklnoqrtuvwx), route each server notice by category, RPL_SNOMASKIS 008; opers default to all and narrow with +s -c etc.

src/modules/connectban.rs

@@ -107,7 +107,7 @@ pub fn on_connect(s: &mut Server, ip: IpAddr) {
         )
         .to_string();
     s.add_xline(XKind::Zline, &glob, dur, &setter, &reason);
-    s.snotice(&format!(
+    s.snotice_c('x', &format!(
         "Connect flooding from IP range {glob} (threshold {threshold})"
     ));
 }