5134 if ZFS_DEBUG or debug= is set, libzpool should enable debug prints

Reviewed by: Adam Leventhal <adam.leventhal@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Saso Kiselkov <skiselkov.ml@gmail.com>
Approved by: Dan McDonald <danmcd@omniti.com>

usr/src/lib/libzpool/common/kernel.c

@@ -629,6 +629,9 @@ dprintf_setup(int *argc, char **argv)
 	 */
 	if (dprintf_find_string("on"))
 		dprintf_print_all = 1;
+
+	if (dprintf_string != NULL)
+		zfs_flags |= ZFS_DEBUG_DPRINTF;
 }
 
 /*