NFSv4: Don't clear capabilities that won't be reset

Don't clear the capabilities that are not going to get reset by the call
to _nfs4_server_capabilities().

Reported-by: Scott Haiden <scott.b.haiden@gmail.com>
Fixes: b01f21ca ("NFS: Fix the setting of capabilities when automounting a new filesystem")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>