LU-5830 scripts: use lustre_rmmod in lnet start/stop script

In lnet's start/stop script stop phase, use lustre_rmmod instead
to try to unload a static list/sequence of modules.

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Change-Id: Ie8584b32e4d7cd21de0ed18954aa38124485964d
Reviewed-on: http://review.whamcloud.com/12513
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Brian J. Murrell <brian.murrell@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>