generic/563: allow read tolerance for f2fs in scenario 3

generic/563: allow read tolerance for f2fs in scenario 3

F2FS is a log-structured file system that allocates new blocks even for
overwrites. To perform allocation, it may need to read metadata blocks
(such as the Node Address Table (NAT) or Segment Info Table (SIT)) if
they are not already in memory.

In scenario 3 (read -> read/write), unlike scenario 2, there is no prior
write in the same mount session to load these metadata blocks into memory.
Therefore, the write operation in the second cgroup triggers metadata
reads, which are charged to that cgroup.

Relax the read tolerance for f2fs in scenario 3 to accommodate these
expected metadata reads, matching the tolerance already used in scenario 2.

Signed-off-by: Jan Prusakowski <jprusakowski@google.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Reviewed-by: Zorro Lang <zlang@kernel.org>
Signed-off-by: Zorro Lang <zlang@kernel.org>