LU-4357 libcfs: restore __GFP_WAIT flag to memalloc calls

LU-4357 libcfs: restore __GFP_WAIT flag to memalloc calls

In 2.4, the flags passed to the memory allocation functions are
translated from CFS enumeration values types to the kernel GFP
values by calling cfs_alloc_flags_to_gfp(). This function adds
__GFP_WAIT to all flags except CFS_ALLOC_ATOMIC. In 2.5, when
the cfs wrappers were dropped, cfs_alloc_flags_to_gfp() was
removed and the CFS_ALLOC_xxxx was simply replaced with __GFP_xxxx.
This means that most memory allocation calls are missing the
__GFP_WAIT flag. The result is that Lustre experiences more ENOMEM
errors, many of which the higher levels of Lustre do not handle
robustly.
Notes GFP_NOFS = __GFP_WAIT | __GFP_IO. So the patch replaces
__GFP_IO with GFP_NOFS.
Patch does not add __GFP_WAIT to GFP_IOFS. GFP_IOFS was not used in
2.4 so it has never been used with __GFP_WAIT.

Signed-off-by: Ann Koehler <amk@cray.com>
Signed-off-by: Emoly Liu <emoly.liu@intel.com>
Change-Id: Ib241b39674129a27fea53c23c8ce3e74d165372a