Make sure the NFS readdir client fills in all "struct dirent" data.

The NFS client code (nfsrpc_readdir() and nfsrpc_readdirplus()) wasn't
filling in parts of the readdir reply, such as d_pad[01] and the bytes
at the end of d_name within d_reclen. As such, data left in a buffer cache
block could be leaked to userland in the readdir reply.
This patch makes sure all of the data is filled in.

Reported by: Thomas Barabosch, Fraunhofer FKIE
Reviewed by: kib, markj
MFC after: 2 weeks