lockd: Introduce new-style XDR functions for NLMv3

lockd: Introduce new-style XDR functions for NLMv3

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_encode() and call_decode() to all XDR encoding functions,
rather than building an xdr_stream in every XDR encoding and decoding
function in the kernel.

To do all of this, rewrite the XDR encoding and decoding functions in
fs/lockd/xdr.c to use xdr_streams.  This makes them more or less
incompatible with server-side XDR helper functions, so break them out
into a separate source file.

Static helper functions are left without the "inline" directive.  This
allows the compiler to choose automatically how to optimize these for
size or speed.

SHARE-related functionality doesn't seem to be used, as those
functions are hiding behind a #define that isn't set anywhere that I
can find.  And, they've been in there forever (at least as far back as
the kernel's git history goes), yet remain unused.  Let's take the
opportunity to bin them.  It should be easy enough for someone to
introduce proper XDR functions if at some point SHARE-related NLM
functionality is desired.

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>