Check for __GFP_RECLAIM instead of GFP_KERNEL

Check for __GFP_RECLAIM instead of GFP_KERNEL because zfs modifies
IO and FS flags which breaks the check for GFP_KERNEL.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Matt Ahrens <matt@delphix.com>
Reviewed-by: Sebastian Gottschall <s.gottschall@dd-wrt.com>
Signed-off-by: Michael Niewöhner <foss@mniewoehner.de>
Closes #9034