Update Dockerfile

Dockerfile

@@ -1,5 +1,6 @@
 ARG BCI_IMAGE=registry.suse.com/bci/bci-base
 ARG GO_IMAGE=rancher/hardened-build-base:v1.21.9b1
+ARG ARCH="amd64"
 FROM --platform=${ARCH} ${BCI_IMAGE} as bci
 FROM --platform=${ARCH} ${GO_IMAGE} as builder
 # setup required packages
@@ -11,7 +12,6 @@ RUN set -x && \
     linux-headers \
     make
 # setup the build
-ARG ARCH="amd64"
 ARG K3S_ROOT_VERSION=v0.13.0
 ADD https://github.com/rancher/k3s-root/releases/download/${K3S_ROOT_VERSION}/k3s-root-xtables-${ARCH}.tar /opt/xtables/k3s-root-xtables.tar
 RUN tar xvf /opt/xtables/k3s-root-xtables.tar -C /opt/xtables