LU-14868 llite: revert 'simplify callback handling for async getattr'

LU-14868 llite: revert 'simplify callback handling for async getattr'

This reverts commit cbaaa7cde45f59372c75577d7274f7e2e38acd24.

This is causing process hangs and timeouts during file removal.

Test-Parameters: trivial
Fixes: cbaaa7cde4 ("LU-14139 llite: simplify callback handling for async getattr")
Change-Id: I77f5bc460850bfe7a5143e22b0c5f3e14a40474a
Reviewed-on: https://review.whamcloud.com/44371
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>