Wrap buffers used for rpc debug printks into RPC_IFDEBUG

Sorry for the noise, but here's the v3 of this compilation fix :)

There are some places, which declare the char buf[...] on the stack
to push it later into dprintk(). Since the dprintk sometimes (if the
CONFIG_SYSCTL=n) becomes an empty do { } while (0) stub, these buffers
cause gcc to produce appropriate warnings.

Wrap these buffers with RPC_IFDEBUG macro, as Trond proposed, to
compile them out when not needed.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Acked-by: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>