Number of NAK packets sent by the receiver transport (LBT-RM, LBT-RU)

- n (Int32)
- Statistics set index

Number of NAK packets sent.

UM batches NAKs into NAK packets to save network bandwidth. This should
always be less than or equal to the number of individual NAKs sent (naksSent,
below).
This method returns a value from the nth set of statistics
encapsulated within this object.