allow additional netmask for MC outgoing interface

src/NameService.cxx

@@ -288,13 +288,16 @@ namespace daq {
 
         boost::asio::ip::address NameService::find_interface(const std::string& netmask)
         {
-            auto addr = boost::asio::ip::address::from_string(netmask).to_v4();
-
-	    // hack to pass additional mask for finding the multicast interface to use
+            std::string local_mask(netmask);
 	    std::string mc_mask("255.255.255.255");
-	    if(getenv("TDAQ_ASYNCMSG_MULTICAST_MASK")) {
-		mc_mask = getenv("TDAQ_ASYNCMSG_MULTICAST_MASK");
-	    }
+
+            auto n = netmask.find('/');
+            if (n != std::string::npos) {
+                local_mask = netmask.substr(0,n);
+                mc_mask = netmask.substr(n+1);
+            }
+
+            auto addr = boost::asio::ip::address::from_string(local_mask).to_v4();
 	    auto mask = boost::asio::ip::address::from_string(mc_mask).to_v4();
 
             auto interfaces = daq::transport::Interface::interfaces();