The reference counting in nfs4_init_client assumes wongly that it
is safe for nfs4_discover_server_trunking() to return a pointer to a
nfs_client prior to bumping the reference count.
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com> Cc: Chuck Lever <chuck.lever@oracle.com> Cc: Ben Greear <greearb@candelatech.com> Cc: stable@vger.kernel.org [>=3.7]