LU-14499 revert: LU-13368 lnet: discard the callback

LU-14499 revert: LU-13368 lnet: discard the callback

The changes introduced by LU-13368 have been shown to cause
the o2iblnd shutdown procedure to hang on lustre_rmmod
as it infinitely waits for peers to disconnect. Revert it.
This reverts commit babf0232273467b7199ec9a7c36047b1968913df.

Lustre-change: https://review.whamcloud.com/41937
Lustre-commit: TBD (from 9a1b64724bdb9452a6c3e14a92c7ef341173d19b)

Signed-off-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Change-Id: I489ae4af445b18df852ec35adc958c4fac33de09
Reviewed-on: https://review.whamcloud.com/42117
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>