ext4: Fix block bitmap inconsistencies after a crash when deleting files

We have experienced bitmap inconsistencies after crash during file
delete under heavy load.  The crash is not file system related and I
the following patch in ext4_free_branches() fixes the recovery
problem.

If the transaction is restarted and there is a crash before the new
transaction is committed, then after recovery, the blocks that this
indirect block points to have been freed, but the indirect block
itself has not been freed and may still point to some of the free
blocks (because of the ext4_forget()).

So ext4_forget() should be called inside ext4_free_blocks() to avoid
this problem.

Signed-off-by: Amir Goldstein <amir73il@users.sf.net>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>