refactor(set_ipv6): replace recursion with while loop

scripts/menus/2_settings.sh

@@ -489,7 +489,10 @@ set_firewall_vm(){
 	setconfig vm_redir $vm_redir
 	setconfig vm_ipv4 "'$vm_ipv4'"
 }
-set_ipv6() { #ipv6设置
+
+# ipv6设置
+set_ipv6() {
+    while true; do
         [ -z "$ipv6_redir" ] && ipv6_redir=OFF
         [ -z "$ipv6_dns" ] && ipv6_dns=ON
         echo "-----------------------------------------------"
@@ -499,7 +502,9 @@ set_ipv6() { #ipv6设置
         echo "-----------------------------------------------"
         read -p "请输入对应数字 > " num
         case "$num" in
-    0) ;;
+        "" | 0)
+            break
+            ;;
         1)
             if [ "$ipv6_redir" = "OFF" ]; then
                 ipv6_support=ON
@@ -510,15 +515,16 @@ set_ipv6() { #ipv6设置
             fi
             setconfig ipv6_redir $ipv6_redir
             setconfig ipv6_support $ipv6_support
-        set_ipv6
             ;;
         2)
             [ "$ipv6_dns" = "OFF" ] && ipv6_dns=ON || ipv6_dns=OFF
             setconfig ipv6_dns $ipv6_dns
-        set_ipv6
             ;;
         *)
             errornum
+            sleep 1
+            break
             ;;
         esac
+    done
 }