xfs: move b_li_list based retry handling to common code

xfs: move b_li_list based retry handling to common code

The dquot and inode version are very similar, which is expected given the
overall b_li_list logic.  The differences are that the inode version also
clears the XFS_LI_FLUSHING which is defined in common but only ever set
by the inode item, and that the dquot version takes the ail_lock over
the list iteration.  While this seems sensible given that additions and
removals from b_li_list are protected by the ail_lock, log items are
only added before buffer submission, and are only removed when completing
the buffer, so nothing can change the list when retrying a buffer.

Signed-off-by: Christoph Hellwig <hch@lst.de>