NFSv4: Rename nfs4_copy_stateid()

It is really a function for selecting the correct stateid to use in a
read or write situation.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

diff --cc fs/nfs/nfs4_fs.h
Simple merge

diff --cc fs/nfs/nfs4proc.c
Simple merge

diff --cc fs/nfs/nfs4state.c
Simple merge

diff --cc fs/nfs/nfs4xdr.c
Simple merge