MT7621 HW NAT Offloading broken

Yes, i have compiled other times but my pc takes many hours and i wanted to be sure which version to use before doing so. This patch is only for disable switch flow control on eth ports that causes (apparently) kernel crash in MT7621. Nothing to do with hardware flow offloading (HW NAT).

I'm looking for a way to enable HW NAT in 19.07 or master branch, otherwise i will compile 18.06.x.