mpm_winnt: remove 'data' AcceptFilter in favor of 'connect'

The 'data' AcceptFilter optimization instructs Windows to wait until
data is received on a connection before completing the AcceptEx
operation. Unfortunately, it seems this isn't performed atomically --
AcceptEx "partially" accepts the incoming connection during the wait for
data, leaving all other incoming connections in the accept queue. This
opens the server to a denial of service.

Since the fix for this requires a substantial rearchitecture (likely
involving multiple outstanding calls to AcceptEx), disable the 'data'
filter for now and replace it with 'connect', which uses the AcceptEx
interface but does not wait for data.

Users running prior releases of httpd on Windows should explicitly move
to a 'connect' AcceptFilter in their configurations if they are
currently using the default 'data' filter.

Many thanks to mludha, Arthur Ramsey, Paul Spangler, and many others for
their assistance in tracking down and diagnosing this issue.

PR: 59970

mpm_winnt: remove the AcceptEx data network bucket

Follow-up to the prior commit: without an incoming data buffer, the
custom network bucket code is now orphaned and we can remove it
entirely. This has the added benefit that we are no longer using the
internal OVERLAPPED.Pointer field, which is discouraged by the MSDN
docs.

mpm_winnt: remove duplication of ap_process_connection

Further follow-up to the previous commit: now that we no longer patch a
network bucket into the brigade, we can revert to calling
ap_process_connection() directly instead of duplicating its logic.

docs: rebuild
Submitted by: jchampion
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1759471 13f79535-47bb-0310-9956-ffa450edef68