Use iter based read/write to support splice and thus sendfile().

The iter based read/write calls can support splice in el9 if we
hook up these calls, otherwise splice will stop working.

->write() similar to: v3.15-rc4-330-g8d0207652cbe. ->read() to
generic implementation.

Signed-off-by: Auke Kok <auke.kok@versity.com>

kmod/src/data.c

@@ -1912,6 +1912,8 @@ const struct file_operations scoutfs_file_fops = {
 #else
 	.read_iter	= scoutfs_file_read_iter,
 	.write_iter	= scoutfs_file_write_iter,
+	.splice_read	= generic_file_splice_read,
+	.splice_write	= iter_file_splice_write,
 #endif
 	.unlocked_ioctl	= scoutfs_ioctl,
 	.fsync		= scoutfs_file_fsync,