fix nginx compilation flags (#8023)
fix nginx compilation flags (#8023)

* use '-O2' instead of '-Og'
  '-O2' produce production optimized binary while '-Og' is used mostly
  for debugging
* use '-mtune=generic' instead of '-mtune=native'
  '-mtune=native' produce optimal code for builder host system, but it
  can be sub-optimal for execution host system
kubernetes/ingress-nginx,kubernetes/ingress-nginx,kubernetes/ingress-nginx,kubernetes/ingress-nginx,kubernetes/ingress-nginx