LU-15885 o2iblnd: fix handling of RDMA_CM_EVENT_UNREACHABLE

LU-15885 o2iblnd: fix handling of RDMA_CM_EVENT_UNREACHABLE

RDMA_CM_EVENT_UNREACHABLE may be received not only when connection
is being connected, but also when it is being closed. Fix handing
of this event accordingly.

Lustre-change: https://review.whamcloud.com/48492
Lustre-commit: 3925b1669d519e6c038ecce1287c1ced3de623d3

Test-Parameters: trivial
Signed-off-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Change-Id: I79428188c159b2d80d36326589b2977db065d4a7
Reviewed-on: https://review.whamcloud.com/c/ex/lustre-release/+/48827
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Frank Sehr <fsehr@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>