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/zdb/zdb.c

@@ -89,6 +89,7 @@
 #include <sys/zstd/zstd.h>
 #include <sys/backtrace.h>
 
+#include <libzpool.h>
 #include <libnvpair.h>
 #include <libzutil.h>
 #include <libzfs_core.h>