NFSv4: Fix the 'nolock' option regression

NFSv4 should just ignore the 'nolock' option. It is an NFSv2/v3 thing...
This fixes the Oops in http://bugzilla.kernel.org/show_bug.cgi?id=13330



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