Add console command to set NewGRF optimiser flags

src/network/network.cpp

@@ -158,6 +158,10 @@ byte NetworkSpectatorCount()
 	return count;
 }
 
+uint NetworkClientCount() {
+	return (uint)NetworkClientInfo::GetNumItems();
+}
+
 /**
  * Change the company password of a given company.
  * @param company_id ID of the company the password should be changed for.

src/network/network_func.h

@@ -37,6 +37,7 @@ extern StringList _network_host_list;
 extern StringList _network_ban_list;
 
 byte NetworkSpectatorCount();
+uint NetworkClientCount();
 bool NetworkIsValidClientName(const std::string_view client_name);
 bool NetworkValidateOurClientName();
 bool NetworkValidateClientName(std::string &client_name);