netsvc: Fix performance of xml-rpc2
netsvc: Fix performance of xml-rpc2

XML-RPCv2 uses the OpenERPDispatcher2 class, which was always calling
the DEBUG_RPC log functions (expensive to prepare), so that ruined its
performance.
Now, user-time to run XML-RPCv2 calls is on-par with XML-RPCv1, again.

xrg/openerp-server,xrg/openerp-server