mkdumprd script contains this fragment:

            echo "deleting routers"
            while route del default gw 0.0.0.0 dev \$interface 2>/dev/null ; do
            done

This won't work in bash, bash requires at least one command in while loop body.
The fix might be:

            echo "deleting routers"
            while route del default gw 0.0.0.0 dev \$interface 2>/dev/null ; do
                :
            done

This is not an urgent problem since busybox shell does accept current form, but for compatibility with other shells it's better to change the script to be bash-compatible.