[PORT] Change port_rates.lua script to prevent display of negative rates

[shiraez]

What I did Fix for: https://github.com/sonic-net/sonic-buildimage/issues/19594 https://github.com/sonic-net/sonic-swss/issues/1892

After changing the speed the counter is reset, We need to reset the <COUNTER_NAME>_last

Why I did it Check if the counter creates an illegal number and then resets it

How I verified it

sudo config interface autoneg Ethernet0 disabled
sudo config interface speed Ethernet0 10
portstat 
sudo config interface speed Ethernet0 100