LU-14962 lnet: Check for -ESHUTDOWN in lnet_parse

LU-14962 lnet: Check for -ESHUTDOWN in lnet_parse

The fix for LU-8106, http://review.whamcloud.com/19993, no longer
works because rc does not have the return value from
lnet_nid2peerni_locked(). Use PTR_ERR to get the return value and
restore the LU-8106 fix.

Lustre-change: https://review.whamcloud.com/44743
Lustre-commit: cce82630cbf2c7badbbdd16a8ca9c8c0065ded13

Test-Parameters: trivial
HPE-bug-id: LUS-10333
Fixes: fa8b4e6357 ("LU-7734 lnet: peer/peer_ni handling adjustments")
Signed-off-by: Chris Horn <chris.horn@hpe.com>
Change-Id: I9cc2bc2d6e675d38cf06d99c524bdd95110bf0e9
Reviewed-on: https://review.whamcloud.com/48487
Reviewed-by: Frank Sehr <fsehr@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>