For #2,
you can change back the mtu to 2K from 4K with using the below command for each physical port:
echo "2048" > /sys/class/net/ib0/device/mlx4_port1_mtu
For #2,
you can change back the mtu to 2K from 4K with using the below command for each physical port:
echo "2048" > /sys/class/net/ib0/device/mlx4_port1_mtu