[tools/bgpscanner] Make isipv4() return 0 explicit

tools/bgpscanner/bgpscanner

@@ -107,7 +107,7 @@ chkint() {
 isip4() {
     for i in 1 2 3 4; do
         case $(printf %s\\n "$1" | cut -d. -f"$i") in
-        [0-9]|[0-9][0-9]|[0-1][0-9][0-9]|2[0-4][0-9]|25[0-5]) ;;
+        [0-9]|[0-9][0-9]|[0-1][0-9][0-9]|2[0-4][0-9]|25[0-5]) return 0;;
         *) return 1;;
         esac
     done