fuse: add FUSE_NO_OPEN_SUPPORT flag to INIT

Here some additional changes to set a capability flag so that clients can
detect when it's appropriate to return -ENOSYS from open.

This amends the following commit introduced in 3.14:

  7678ac50615d  fuse: support clients that don't implement 'open'

However we can only add the flag to 3.15 and later since there was no
protocol version update in 3.14.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: <stable@vger.kernel.org> # v3.15+
diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index 5ca874f..03246cd 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -935,7 +935,7 @@
 		FUSE_SPLICE_WRITE | FUSE_SPLICE_MOVE | FUSE_SPLICE_READ |
 		FUSE_FLOCK_LOCKS | FUSE_IOCTL_DIR | FUSE_AUTO_INVAL_DATA |
 		FUSE_DO_READDIRPLUS | FUSE_READDIRPLUS_AUTO | FUSE_ASYNC_DIO |
-		FUSE_WRITEBACK_CACHE;
+		FUSE_WRITEBACK_CACHE | FUSE_NO_OPEN_SUPPORT;
 	req->in.h.opcode = FUSE_INIT;
 	req->in.numargs = 1;
 	req->in.args[0].size = sizeof(*arg);