app/testpmd: fix Tx scheduling interval

app/testpmd: fix Tx scheduling interval

The first "set txtimes" command parameter specifies the time
interval between scheduled send bursts for single queue. This
interval should be the same for all the forwarding ports.
It requires to maintain the timing related variables on per
queue basis instead of per core, as currently implemented.
This resulted in wrong burst intervals if two or more cores
were generating the scheduled traffic for two or more ports
in txonly mode.

This patch moves the timing variable to the fstream structure.
Only txonly forwarding mode with enabled send scheduling is
affected.

Fixes: 4940344dab1d ("app/testpmd: add Tx scheduling command")
Cc: stable@dpdk.org
Signed-off-by: Viacheslav Ovsiienko <viacheslavo@nvidia.com>
Acked-by: Ferruh Yigit <ferruh.yigit@intel.com>