Increase default CQ count from 1 to num_cpus

include/grpc++/server_builder.h

@@ -195,7 +195,10 @@ class ServerBuilder {
 
   struct SyncServerSettings {
     SyncServerSettings()
-        : num_cqs(1), min_pollers(1), max_pollers(2), cq_timeout_msec(10000) {}
+        : num_cqs(gpr_cpu_num_cores()),
+          min_pollers(1),
+          max_pollers(2),
+          cq_timeout_msec(10000) {}
 
     // Number of server completion queues to create to listen to incoming RPCs.
     int num_cqs;