Add a rq_sendfile_ok flag to svc_rqst which will be cleared in the privacy
case so that the wrapping code will get copies of the read data instead of
real page cache pages.  This makes life simpler when we encrypt the response.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>