s3:rpc_server/svcctl: fix valgrind bugs in _svcctl_QueryServiceConfig2W()

s3:rpc_server/svcctl: fix valgrind bugs in _svcctl_QueryServiceConfig2W()

r->out.buffer needs to stay in its size, as it will be marshalled completely.
As it's preallocated and initialized with zeros, we just need to copy
the payload into it.

If we always marshall the return buffer, we already have the needed
buffer size and don't need to call ndr_size_* functions.

metze
(cherry picked from commit 11683ccf3e68606ecb1cdfa455f7921b119803c6)