LU-18114 lctl: split "lctl net_drop_*" group into subcommands

LU-18114 lctl: split "lctl net_drop_*" group into subcommands

Split "lctl net_drop_*" command group into subcommands, e.g.
"lctl net_drop_add" to "lctl net_drop add".
Also, sanity-lnet.sh is modified to verify this patch.

Test-Parameters: trivial testlist=sanity-lnet
Signed-off-by: Emoly Liu <emoly@whamcloud.com>
Change-Id: I5094328435e5b93a8a7311f26ec77275211e0517
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/56154
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Chris Horn <chris.horn@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>