staging/lustre/osc: some cleanup to reduce stack overflow chance

ptlrpcd_add_req() will wake_up other process, do not hold a spinlock
before calling ptlrpcd_queue_work()->ptlrpcd_add_req().

If current process is allocating memory, memory shrinker could get to
osc_lru_del(), don't call osc_lru_shrink() further since it could
lead a long calling chain.

Use static string OES_STRINGS in OSC_EXTENT_DUMP() to reduce stack
footprint.

Alloc crattr on heap for osc_build_rpc() to reduce stack footprint.

Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3281
Lustre-change: http://review.whamcloud.com/6270


Signed-off-by: Bobi Jam <bobijam.xu@intel.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Keith Mannthey <keith.mannthey@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Peng Tao <tao.peng@emc.com>
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>