pid1: set org.freedesktop.systemd1 as sender service name for direct connections

This way, clients can install the very same match on direct and broker
connections as in both cases the messages will originate from the o.f.s1
service.

src/core/dbus.c

@@ -682,6 +682,12 @@ static int bus_on_connection(sd_event_source *s, int fd, uint32_t revents, void
                 return 0;
         }
 
+        r = sd_bus_set_sender(bus, "org.freedesktop.systemd1");
+        if (r < 0) {
+                log_warning_errno(r, "Failed to set direct connection sender: %m");
+                return 0;
+        }
+
         r = sd_bus_start(bus);
         if (r < 0) {
                 log_warning_errno(r, "Failed to start new connection bus: %m");