LU-10185 gnilnd: change default credits

LU-10185 gnilnd: change default credits

It has been found that a credit value of 64 reduces likelihood of file
io induced congestion without producing performance degradation when a
many router single compute pattern occurs.
Change default compute credits to 64 based on this finding.

Test-parameters: trivial

Signed-off-by: Chris Horn <hornc@cray.com>
Change-Id: I0a1f46bdb2c327a7e6dc9eeb145fe1418d691da1
Reviewed-on: https://review.whamcloud.com/29896
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Shimek <knathrak@gmail.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Doug Oucharek <dougso@me.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>