s4:lib/http: let http_read_response_send/recv() also consume the body if it fits...

s4:lib/http: let http_read_response_send/recv() also consume the body if it fits into a max value

We need to consume full HTTP responses from the socket during the
authentication exchanges, otherwise our HTTP parser gets out of sync for
the next requests.

This will be important for gensec mechs which use an even number
for authentication packets.

I guess this should be done just based on the Content-Length value and
not based on the response code.

So far I saw bodies with 200 and 401 codes.

Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Andreas Schneider <asn@samba.org>