Now IS_DNODE is used in f2fs_flush_inline_data and it has some problems:
1. Just only inodes may include inline data,not all direct nodes
2. When system IO is busy, it is inefficient to lock a direct node page
but not an inode page. Besides, if this direct node page is being
locked by others for IO, f2fs_flush_inline_data will be blocked here,
which will affects the checkpoint process, this is unreasonable.
So IS_INODE should be used in f2fs_flush_inline_data.
Signed-off-by: Zhiguo Niu <zhiguo.niu@xxxxxxxxxx>