LU-56 lnet: eliminate a few locking dance in LNet

LU-56 lnet: eliminate a few locking dance in LNet

This patch gets rid of a few unnecessary locking dance from
LNet, also changed type of lnet_ni_t::ni_last_alive from jiffy to
second because per-second checking should be good enough.

Signed-off-by: Liang Zhen <liang@whamcloud.com>
Change-Id: I0e3269f0a5ae0cfecd9611584d5e213a670e38f6
Reviewed-on: http://review.whamcloud.com/2933
Tested-by: Hudson
Reviewed-by: Doug Oucharek <doug@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Bobi Jam <bobijam@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>