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

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>

References:
  https://www.illumos.org/projects/illumos-gate/issues/5134
  https://github.com/illumos/illumos-gate/commit/7fa49ea

Porting notes:
  Added dprintf_setup() to main in zfs_main.c and zpool_main.c.

Ported by: Turbo Fredriksson <turbo@bayour.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2669

cmd/zfs/zfs_main.c

@@ -6661,6 +6661,8 @@ main(int argc, char **argv)
 	(void) setlocale(LC_ALL, "");
 	(void) textdomain(TEXT_DOMAIN);
 
+	dprintf_setup(&argc, argv);
+
 	opterr = 0;
 
 	/*

cmd/zpool/zpool_main.c

@@ -5879,6 +5879,8 @@ main(int argc, char **argv)
 	(void) setlocale(LC_ALL, "");
 	(void) textdomain(TEXT_DOMAIN);
 
+	dprintf_setup(&argc, argv);
+
 	opterr = 0;
 
 	/*

lib/libzpool/kernel.c

@@ -837,6 +837,9 @@ dprintf_setup(int *argc, char **argv)
 	 */
 	if (dprintf_find_string("on"))
 		dprintf_print_all = 1;
+
+	if (dprintf_string != NULL)
+		zfs_flags |= ZFS_DEBUG_DPRINTF;
 }
 
 /*