LU-13764 lnet: Clear lp_dc_error when discovery completes

LU-13764 lnet: Clear lp_dc_error when discovery completes

If discovery completes successfully then we can clear the
lp_dc_error.

Test-Parameters: trivial
HPE-bug-id: LUS-9081
Signed-off-by: Chris Horn <chris.horn@hpe.com>
Change-Id: If709022c5c4ba0ab8f01b3f4b508ed464fd0b6ff
Reviewed-on: https://review.whamcloud.com/39348
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Amir Shehata <ashehata@whamcloud.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: Oleg Drokin <green@whamcloud.com>