LU-13662 lnet: handle undefined parameters

LU-13662 lnet: handle undefined parameters

If peer_tx_credits or peer_credits are 0, they should be
defaulted to the system defaults 8 and 256 respectively

Signed-off-by: Amir Shehata <ashehata@whamcloud.com>
Change-Id: I351ff37cba0a9adaa1a6c25ff9c7da701724db2b
Reviewed-on: https://review.whamcloud.com/38894
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>