Partially fix breakage following:

https://veyron-review.googlesource.com/#/c/6278/

but a further fix is needed for:

https://veyron-review.googlesource.com/#/c/6373/

Change-Id: I1da390497ad28ff3a0f5b7a420cfb0eb923d4d95
diff --git a/runtimes/google/ipc/benchmarks/server.go b/runtimes/google/ipc/benchmarks/server.go
index b01f59f..36cfdb8 100644
--- a/runtimes/google/ipc/benchmarks/server.go
+++ b/runtimes/google/ipc/benchmarks/server.go
@@ -12,11 +12,11 @@
 type impl struct {
 }
 
-func (i *impl) Echo(ctx ipc.ServerContext, payload []byte) ([]byte, error) {
+func (i *impl) Echo(ctx ipc.ServerCall, payload []byte) ([]byte, error) {
 	return payload, nil
 }
 
-func (i *impl) EchoStream(ctx ipc.ServerContext, stream BenchmarkServiceEchoStreamStream) error {
+func (i *impl) EchoStream(ctx ipc.ServerCall, stream BenchmarkServiceEchoStreamStream) error {
 	rStream := stream.RecvStream()
 	sender := stream.SendStream()
 	for rStream.Advance() {