vhost-local.m4: Fix missing newline.

I left a trap for myself: the extra-stuff argument to the
`USER_SPAMLIMIT_ROUTERS' macro wants a trailing newline (and tab);
otherwise the following material ends up following without a line break.

This went badly wrong: a `condition = ' line was extended with extra
material causing it to always match!  Fortunately little harm was
actually done.