Remove kmem_set_warning() interface replace with __GFP_NOWARN flag.

Remove kmem_set_warning() interface replace with __GFP_NOWARN flag.

Remove the kmem_set_warning() hack used by the kmem-splat regression
tests with a per-allocation flag called __GFP_NOWARN.  This matches
the lower level linux flag of similar by slightly different function.
The idea is you can then explicitly set this flag on requests where
you know your breaking the max 8k rule but you need/want to do it
anyway.

This is currently used by the regression tests where we intentionally
push things to the limit but don't want the log noise.  Additionally,
we are forced to use it in spl_kmem_cache_create() because by default
NR_CPUS is very large and theres no easy way to handle that.

Finally, I've added a stack_dump() call to the warning when it is
trigger to make to clear exactly where the allocation is taking place.