cifs: copy_file_range needs to strip setuid bits and update timestamps

cifs has both source and destination inodes locked throughout the copy.
Like ->write_iter(), we update mtime and strip setuid bits of destination
file before copy and like ->read_iter(), we update atime of source file
after copy.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Steve French <stfrench@microsoft.com>