Set ipflush_onchange on gtw node of os-ha-ovs model

This patch sets ipflush_onchange: True for interfaces of gateway
node of os-ha-ovs model.
Without this parameters Salt cannot remove address from interfaces
properly.

Related-PROD: PROD-16793

Change-Id: I374a695f3f5d83b76b26d445615c71fc0b382e59
12 files changed