staging/lustre/mdc: Keep resend FLocks

FLocks requests (particulary F_UNLCKs) can't be trashed
upon comm problems with Server/MDS nor upon kill/exit,
thus we need to keep retry/send.

Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-2665
Lustre-change: http://review.whamcloud.com/6415


Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Reviewed-by: Bobi Jam <bobijam@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: Peng Tao <tao.peng@emc.com>
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>