NFSv4: Fix a race in NFSv4.1 server trunking discovery

We do not want to allow a race with another NFS mount to cause
nfs41_walk_client_list() to establish a lease on our nfs_client before
we're done checking for trunking.

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

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

diff --cc fs/nfs/nfs4client.c
Simple merge

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