staging: lustre: osc: limits the number of chunks in write RPC

OSC has to make sure that it won't issue write RPCs with too many
chunks otherwise it will casue ZFS to create transactions much
bigger than DMU_MAX_ACCESS in size, which will end up with write
failure.

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Signed-off-by: Dmitry Eremin <dmitry.eremin@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-8135
Reviewed-on: http://review.whamcloud.com/22369
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-8632
Reviewed-on: http://review.whamcloud.com/22654


Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Patrick Farrell <paf@cray.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>