LU-14668 lnet: don't delete peer created by Lustre

LU-14668 lnet: don't delete peer created by Lustre

Peers created by Lustre have their primary NIDs locked.
If that peer is deleted, it'll confuse lustre. So when manually
deleting a peer using:
   lnetctl peer del --prim_nid ...
We must continue to preserve the primary NID. Therefore we delete
all the constituent NIDs, but keep the primary NID. We then
flag the peer for rediscovery.

Signed-off-by: Amir Shehata <ashehata@whamcloud.com>
Change-Id: I34eef9b0049435a01fde87dc8263dd50f631c551
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/43565
Tested-by: Maloo <maloo@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Reviewed-by: Cyril Bordage <cbordage@whamcloud.com>