LU-2433 lnet: enable asymmetric router failure detection

LU-2433 lnet: enable asymmetric router failure detection

Asynmmetric router failure detection is disabled by default,
it's helpful to enable it by default.
The original change is at https://github.com/chaos/lustre/
commit/872bfc41cc858a6c01cae3648e0ca329a414a436

Signed-off-by: Christopher J. Morrone <morrone2@llnl.gov>
Signed-off-by: Emoly Liu <emoly.liu@intel.com>
Change-Id: I259e00911cdf3d7caecb98c9832d40a91b571596
Reviewed-on: http://review.whamcloud.com/4753
Reviewed-by: Isaac Huang <he.huang@intel.com>
Reviewed-by: Liang Zhen <liang.zhen@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>