Turn on both PF_FSTRANS and PF_MEMALLOC_NOIO in spl_fstrans_mark

Turn on both PF_FSTRANS and PF_MEMALLOC_NOIO in spl_fstrans_mark

In b4ad50a, we abandoned memalloc_noio_save in favor of spl_fstrans_mark
because earlier kernel with it doesn't turn off __GFP_FS. However, for newer
kernel, we would prefer PF_MEMALLOC_NOIO because it would work for allocation
in kernel which we cannot control otherwise. So in this patch, we turn on both
PF_FSTRANS and PF_MEMALLOC_NOIO in spl_fstrans_mark.

Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #523