mod_ratelimit: Don't interfere with "chunked" encoding.

By the time ap_http_header_filter() sends the header brigade and adds the
"CHUNK" filter, we need to garantee that the header went through all the
filters' stack, and more specifically above ap_http_chunk_filter() which
assumes that all it receives is content data.
Since rate_limit_filter() may retain the header brigade, make it run after
ap_http_chunk_filter(), just before AP_FTYPE_CONNECTION filters.

Also, ap_http_header_filter() shouldn't eat the EOS for HEAD/no-body responses.
For instance mod_ratelimit depends on it since r1835168, but any next request
filter may as well to flush and/or bail out approprietely.

This fixes the regression introduced in 2.4.34 (r1835168).
PR 62568.

Submitted by: ylavic
Reviewed by: covener, ylavic, jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1839497 13f79535-47bb-0310-9956-ffa450edef68