NFS: inter ssc open

NFSv4.2 inter server to server copy requires the destination server to
READ the data from the source server using the provided stateid and
file handle.

Given an NFSv4 stateid and filehandle from the COPY operaion, provide the
destination server with an NFS client function to create a struct file
suitable for the destiniation server to READ the data to be copied.

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