util.pread2(['ebtables', '-A', vm_chain, '-i', vif, '-s', '!', vm_mac, '-j', 'DROP'])
if user changes the VM mac address, all egress packet from the VM will be dropped, but the egress packet still contaminate the bridge cache with fake MAC,
This patch moves the rule to ebtables nat table PREROUTING chain, then the egress packet with modified MAC will not contaminate the bridge cache.
Anthony
CS-14902: Fixing ovs-vif-flows.py for avoiding it kicks in with exp backoff timeouts if ovs is not running
Also removing unnecessary copies of the same script