nfs42: client needs to strip file mode's suid/sgid bit after ALLOCATE op

The Linux NFS server strips the SUID and SGID from the file mode
on ALLOCATE op.

Modify _nfs42_proc_fallocate to add NFS_INO_REVAL_FORCED to
nfs_set_cache_invalid's argument to force update of the file
mode suid/sgid bit.

Suggested-by: Trond Myklebust <trondmy@hammerspace.com>
Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Tested-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>