tcptop TX_KB always gives 0 values

OS environment: centos7
Kenrel version: 3.10.0-1062.12.1.el7.x86_64
bcc tools: version 11 and 12 both.

tcpop TX_KB field always gives 0 TX_KB. RX_RB is right value.
tcplife gives right values though.

we can repro with traffic or scp of last file back and forth.

Start by reproducing the report through the tcptop entry point on CentOS 7 with the stated kernel, using traffic or scp in both directions. Compare the TX_KB and RX_RB output with tcplife, and consider the issue complete when transmitted values are reported correctly and the behavior is covered by an appropriate check.

Written by the indexing model from the issue text.