core: use uniform style for RateLimit initialization

RateLimit is designed so that we can always initialize only the first two
fields explicitly. All other call sites use a single line for this.

src/core/socket.c

@@ -100,8 +100,7 @@ static void socket_init(Unit *u) {
         s->control_pid = PIDREF_NULL;
         s->control_command_id = _SOCKET_EXEC_COMMAND_INVALID;
 
-        s->trigger_limit.interval = USEC_INFINITY;
-        s->trigger_limit.burst = UINT_MAX;
+        s->trigger_limit = RATELIMIT_OFF;
 
         s->poll_limit_interval = USEC_INFINITY;
         s->poll_limit_burst = UINT_MAX;