LU-6142 lustre: change super/file/inode operations to const

LU-6142 lustre: change super/file/inode operations to const

All 'struct file_operations', 'struct inode_operations', 'struct
export_operations' and 'struct super_operations' are changed to
'const'.  This potenetially allows them to be placed in read-only
memory, and ensure they are never changed.

Test-Parameters: trivial
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: I8b236f0248eca11f91f11da02fe18be3f6d2e17c
Reviewed-on: https://review.whamcloud.com/39394
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>