ext4: update fast commit TODOs

This series takes care of a couple of TODOs and adds new ones. Update
the TODOs section to reflect current state and future work that needs
to happen.

Signed-off-by: Harshad Shirwadkar <harshadshirwadkar@gmail.com>
Link: https://lore.kernel.org/r/20211223202140.2061101-5-harshads@google.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>