Fix run-server script interface option issue

scripts/run-server

@@ -88,7 +88,7 @@ while getopts "a:b:chtx:X:d:i:g:I:T:E:P:B:" opt; do
 	make_opts=" -e WITH_XDP=1"
         ;;
     I )
-        interface+="${OPTARG}"
+        interface="${OPTARG}"
       ;;
     X )
         server_options+=" -x ${OPTARG}"