NFS: Introduce new-style XDR decoding functions for NFSv2

We'd like to prevent local buffer overflows caused by malicious or
broken servers.  New xdr_stream style decoders can do that.

For efficiency, we also eventually want to be able to pass xdr_streams
from call_decode() to all XDR decoding functions, rather than building
an xdr_stream in every XDR decoding function in the kernel.

Static helper functions are left without the "inline" directive.  This
allows the compiler to choose automatically how to optimize these for
size or speed.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Tested-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

include/linux/nfs3.h

@@ -13,6 +13,7 @@
 #define NFS3_COOKIESIZE		4
 #define NFS3_CREATEVERFSIZE	8
 #define NFS3_COOKIEVERFSIZE	8
+#define NFS3_WRITEVERFSIZE	8
 #define NFS3_FIFO_DEV		(-1)
 #define NFS3MODE_FMT		0170000
 #define NFS3MODE_DIR		0040000