remove ipcalc, add mask3cdr instead

Dockerfile

@@ -2,7 +2,9 @@ FROM alpine:3.12.0
 
 ARG KUBECTL_VERSION=1.18.9
 
-RUN apk add --update --no-cache curl ca-certificates jq ipcalc && \
+COPY mask2cdr /usr/sbin/
+
+RUN apk add --update --no-cache curl ca-certificates jq && \
     curl -LO https://storage.googleapis.com/kubernetes-release/release/v${KUBECTL_VERSION}/bin/linux/amd64/kubectl && \
     mv kubectl /usr/bin/kubectl && \
     chmod +x /usr/bin/kubectl

mask2cdr

@@ -0,0 +1,5 @@
+   # Assumes there's no "255." after a non-255 byte in the mask
+   x=${1##*255.}
+   set -- 0^^^128^192^224^240^248^252^254^ $(( (${#1} - ${#x})*2 )) ${x%%.*}
+   x=${1%%$3*}
+   echo $(( $2 + (${#x}/4) ))