LU-8071 ldiskfs: handle system freeze protection

LU-8071 ldiskfs: handle system freeze protection

For RHEL6 2.6.32, or kernel 3.6 or newer, it supports wrapped
functions for filesystem freeze protection, such as sb_{start,
stop}_write(). Usually, they are called by VFS. Since Lustre
uses ldiskfs backend bypass VFS layer, it is the OSD's duty to
handle filesystem freeze protection by calling related wrapped
filesystem freeze protection functions. As for other kernel,
such as 3.0.101, related logic has been handled inside ldiskfs
via vfs_check_frozen().

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: Idb2b4ca02d569ec818a06b534e857b6ee44f89a2
Reviewed-on: http://review.whamcloud.com/20062
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Wang Shilong <wshilong@ddn.com>