NFS: for "inter" copy treat ESTALE as ENOTSUPP

If the client sends an "inter" copy to the destination server but
it only supports "intra" copy, it can return ESTALE (since it
doesn't know anything about the file handle from the other server
and does not recognize the special case of "inter" copy). Translate
this error as ENOTSUPP and also send OFFLOAD_CANCEL to the source
server so that it can clean up state.

Signed-off-by: Olga Kornievskaia <kolga@netapp.com>