LU-9680 lnet: Empty route/peer table is not an error

LU-9680 lnet: Empty route/peer table is not an error

lnetctl peer/route show command, without any other arguments,  should
not return an error if the peer/route tables are empty. If the user
specifies a particular peer/route to show, and that peer/route does
not exist then this is an error.

Modify the dumpit routines to check the netlink message length to
determine whether the user supplied any arguments to the show
commands, and use this information to return the proper status. Some
dead code was also removed from lnet_route_show_dump().

We also fix an issue with older kernels where non-zero return status
from old dumpit commands was not being returned correctly.

Test-Parameters: trivial
Signed-off-by: Chris Horn <chris.horn@hpe.com>
Change-Id: I9a188c573b0f373052208dbea52ea56181719769
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/53366
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>