Man pages matching name tshttptxnclientpacketdscpset in section 3ts:

TSHttpTxnClientPacketDscpSet.3ts.en	debian 10 / trafficserver-dev
TSHttpTxnClientPacketDscpSet.3ts.en	debian 11 / trafficserver-dev
TSHttpTxnClientPacketDscpSet.3ts.en	debian 12 / trafficserver-dev