Number of datagrams currently queued by the rate limiter (LBT-RM only).

- n (Int32)
- Statistics set index

Number of datagrams currently queued by the rate limiter.

When a source transport attempts to send messages (any type) faster than its
data rate limiter allows (set by configuration option
transport_lbtrm_data_rate_limit, default 10Mbps), the data rate limiter queues
the messages until they can be sent within the data rate limit.
This method returns a value from the first
set of statistics encapsulated within this object
and would normally be used when the object has been
created using a specific source to instantiate the class.