config: Reduce DRAM controller regression traffic rate
config: Reduce DRAM controller regression traffic rate

This patch changes the traffic generator period such that it does not
completely saturate the DRAM controller and create an ever-growing
backlog in the queued port.

A separate patch updates the stats.

LingxiaoJIA/gem5,haowu4682/gem5,haowu4682/gem5,LingxiaoJIA/gem5,haowu4682/gem5,LingxiaoJIA/gem5,LingxiaoJIA/gem5,haowu4682/gem5,haowu4682/gem5,haowu4682/gem5,LingxiaoJIA/gem5,haowu4682/gem5,LingxiaoJIA/gem5,haowu4682/gem5,LingxiaoJIA/gem5,haowu4682/gem5