NFS: Fix a potential data corruption

In the Linux kernel, the following vulnerability has been resolved: NFS: Fix a potential data corruption We must ensure that the subrequests are joined back into the head before we can retransmit a request. If the head was not on the commit lists, because the server wrote it synchronously, we still need to add it back to the retransmission list. Add a call that mirrors the effect of nfs_cancel_remove_inode() for O_DIRECT.