Don't clamp write3 max to 32k

We use our own XDR and RPC layer nowadays and do not have
any external dependencies to XDR or RPC.

As such we no longer need to clamp the write size to max 32kb
since we never link to the system rpc/xdr libraries.
(and thus dont have to clamp in case the system library is broken for
pdu's > 32k)

Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>