xfs: rearrange code in xfs_inode_item_precommit

There are similar extsize checks and updates done inside and outside
the inode item lock, which could all be done under a single top
level logic branch outside the ili_lock. The COW extsize fixup can
potentially miss updating the XFS_ILOG_CORE in ili_fsync_fields, so
moving this code up above the ili_fsync_fields update could also be
considered a fix.

Further, to make the next change a bit cleaner, move where we
calculate the on-disk flag mask to after we attach the cluster
buffer to the the inode log item.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>