LU-14095 ssk: default rounds of Miller-Rabin for DH_check

LU-14095 ssk: default rounds of Miller-Rabin for DH_check

OpenSSL 1.1.1c increased the number of rounds used for Miller-Rabin
testing of the prime provided as input parameter to DH_check(). This
makes the check roughly x10 longer, and can lead to request timeouts
when an SSK flavor is being used.

Instead, use a dynamic number of rounds based on the speed of the
check, evaluated when the lsvcgssd daemon starts. If DH_check()
runtime is fine, just use it instead of our own check.

Test-Parameters: clientdistro=el8.2 serverdistro=el8.2 testgroup=review-dne-ssk
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: Id392cdd76ede196094b146c68d230bc52852aa34
Reviewed-on: https://review.whamcloud.com/40686
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>