renderer: s/format_size/render_size/

renderer: s/format_size/render_size/

format_size is the "lower" level helper and is not fit (anymore) to
be set as renderer directly, as its parameter signature may clash
with the extra, different ones, that renderers get passed.

For example, the useSI param always gets evaluated as true due to
the metaData "truthy" value that calls to a renderer get passed along
most of the time.

Use the render_size instead, a wrapper which only passes along value
to format_size.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>