Tweak the AP_MIN_SENDFILE_BYTES. Not using sendfile on Windows

Tweak the AP_MIN_SENDFILE_BYTES.  Not using sendfile on Windows
in the general (non byterange) case is a HUGE performance hit (> 50% in many cases).
I also suspect most byterange requests will be for substantially more bytes (a pageful
out of a larger document for example). In the uncommon (I believe) cases where
fewer bytes are requested, 250 bytes per packet is not too abusive of the network.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@87983 13f79535-47bb-0310-9956-ffa450edef68