ZTS: Optimize KSM on Linux and remove it for FreeBSD

Don't use KSM on the FreeBSD VMs and optimize KSM settings for
Linux to have faster run times.

Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Tino Reichardt <milky-zfs@mcmilk.de>
Closes #17247

.github/workflows/scripts/qemu-8-summary.sh

@@ -45,7 +45,7 @@ fi
 
 echo -e "\nFull logs for download:\n    $1\n"
 
-for i in $(seq 1 $VMs); do
+for ((i=1; i<=VMs; i++)); do
   rv=$(cat vm$i/tests-exitcode.txt)
 
   if [ $rv = 0 ]; then