LU-18110 doc: lctl multiple NIDs specification not clear

LU-18110 doc: lctl multiple NIDs specification not clear

The original statement is somewhat confusing. I think
this one is better, but may be there's an even better
option somebody could think of?

Test-Parameters: trivial
Change-Id: I4206269913eaec06fec034374da2be42625086b0
Signed-off-by: Oleg Drokin <green@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/55957
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>