libzpool: separate driver-side include

Sponsored-by: https://despairlabs.com/sponsor/
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes #17861

cmd/raidz_test/raidz_test.c

@@ -33,6 +33,7 @@
 #include <sys/vdev_raidz_impl.h>
 #include <assert.h>
 #include <stdio.h>
+#include <libzpool.h>
 #include "raidz_test.h"
 
 static int *rand_data;