Previously, unless HAVE_TCP_KEEP was defined equally for varnishd
and an API client (vmod), the latter used a wrong struct declaration
and, consequently, struct params members were accessed at a wrong
location. This could have adverse effects from reading bogus
values to overwriting wrong parameters or other memory.

For consistency, we keep uninplemented parameters also in the
cli and rst output with an appropriate description.

Setting them over the cli is not an error, but has no effect.