LU-13071 lnet: reduce log severity for health events

LU-13071 lnet: reduce log severity for health events

No need to print an error when the health of an interface is
reduced. Changed it to debug level.

Test-Parameters: trivial
Signed-off-by: Amir Shehata <ashehata@whamcloud.com>
Change-Id: Ia60ade12efab732ea4b0388a3803976bf65938ab
Reviewed-on: https://review.whamcloud.com/37002
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>