fsck.ubifs: Ensure that TNC LEB can be scanned successful

fsck.ubifs: Ensure that TNC LEB can be scanned successful

This is the second part of 6/18 step in fsck. Add an extra checking for
non-check mode while traversing TNC, make sure that all LEBs(contains TNC)
can be scanned successful. There could be following steps and possible
errors:
 Step 2. Scan all LEBs(contain TNC), remove TNC branch which points to
 corrupted LEB.
  a. corrupted node is found by scanning: If current node is index node,
     danger mode with rebuild_fs and normal mode with 'yes' answer will
     turn to rebuild filesystem, other modes will exit; If current node
     is non-index node, danger mode and normal mode with 'yes' answer
     will remove all TNC branches which point to the corrupted LEB,
     other modes will exit.
  b. LEB contains both index and non-index nodes: danger mode with
     rebuild_fs and normal mode with 'yes' answer will turn to rebuild
     filesystem, other modes will exit.
This is a preparation for space checking, which means that ubifs_scan
will always succeed when check properties for any TNC LEBs. We do this
before checking files(step 7) & extracting dentry tree(step 8), nodes
cannot be dropped(which may corrupted file and make file inconsistent
again) when scanning corrupted as long as the dentry tree is extracted.

Signed-off-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: David Oberhollenzer <david.oberhollenzer@sigma-star.at>