NFSD: add trace points to track server copy progress

Add trace points on destination server to track inter and intra
server copy operations.

Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
Tested-by: Chen Hanxiao <chenhx.fnst@fujitsu.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>