fuse: add missing FR_FORCE

fuse: add missing FR_FORCE

commit 2e38bea99a80eab408adee27f873a188d57b76cb upstream.

fuse_file_put() was missing the "force" flag for the RELEASE request when
sending synchronously (fuseblk).

If this flag is not set, then a sync request may be interrupted before it
is dequeued by the userspace filesystem.  In this case the OPEN won't be
balanced with a RELEASE.

Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Fixes: 5a18ec176c93 ("fuse: fix hang of single threaded fuseblk filesystem")
[bwh: Backported to 3.2:
 - "force" flag is a bitfield
 - Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>