NFS: Optimise attribute revalidation on close().
NFS: Optimise attribute revalidation on close().

 Only force a getattr in nfs_file_flush() if the attribute
 cache is stale.

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

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas