fix(avahi): avoid restart on transient iface loss

Purpose of the change:
- Keep Avahi running when an allowed interface temporarily loses carrier or its address.

Before this change:
- rc.avahidaemon update recomputed active bindings and restarted Avahi whenever the active bind list differed from allow-interfaces.
- DHCP/network hooks could therefore restart Avahi while a wireless interface was still down.

Why that was a problem:
- Avahi already observes interface loss and recovery while running.
- Restarting during a temporary outage can start Avahi with no suitable network protocol, causing it to exit and remain stopped.

What the new change accomplishes:
- Avoids restarting Avahi when the only bind difference is an allowed interface that is currently inactive.
- Still restarts when an active interface is newly added to the bind list or an active interface is deliberately removed.

How it works:
- rc.avahidaemon update compares current and recomputed bind lists.
- The restart decision now checks whether changed interfaces are active before calling avahid_restart.

Author: elibosley

etc/rc.d/rc.avahidaemon

@@ -119,8 +119,52 @@ avahid_reload(){
   fi
 }
 
+# Avahi observes interface loss/recovery while running. Restart only for bind
+# changes that add an active interface or remove an interface that is still
+# active; do not restart just because an allowed interface temporarily vanished.
+csv_has(){
+  local LIST=",$1,"
+  [[ $LIST == *",$2,"* ]]
+}
+
+iface_active(){
+  [[ -n $(show dev "$1") ]]
+}
+
+bind_adds_active_iface(){
+  local CURRENT="$1" NEXT="$2" IFACE
+  IFS=, read -ra IFACES <<< "$NEXT"
+  for IFACE in "${IFACES[@]}"; do
+    [[ -n $IFACE ]] || continue
+    if ! csv_has "$CURRENT" "$IFACE"; then
+      return 0
+    fi
+  done
+  return 1
+}
+
+bind_removes_active_iface(){
+  local CURRENT="$1" NEXT="$2" IFACE
+  IFS=, read -ra IFACES <<< "$CURRENT"
+  for IFACE in "${IFACES[@]}"; do
+    [[ -n $IFACE ]] || continue
+    if ! csv_has "$NEXT" "$IFACE" && iface_active "$IFACE"; then
+      return 0
+    fi
+  done
+  return 1
+}
+
+bind_requires_restart(){
+  bind_adds_active_iface "$1" "$2" || bind_removes_active_iface "$1" "$2"
+}
+
 avahid_update(){
-  if avahid_running && check && [[ "$(this allow-interfaces)" != "$BIND" ]]; then
+  local CURRENT
+  if avahid_running && check; then
+    CURRENT="$(this allow-interfaces)"
+    [[ "$CURRENT" != "$BIND" ]] || return 0
+    bind_requires_restart "$CURRENT" "$BIND" || return 0
     log "Updating $DAEMON..."
     avahid_restart # note we need restart here, not reload in order to update interfaces
   fi