Revert "nfscl: Do not do readahead for directories"

The PR reported hangs that were avoided when this commit was
reverted. Since it was only a cleanup, revert it.
The LORs in the PR need further investigation, since I think
readahead only hides the problem.

PR: 279138
This reverts commit fbe965591f8a0a32c805a279a2505d4c20d22d26.