[Enhancement] come up with a less destructive way to deal with current_RouterConfiguration FULL message_type update

[er1cthe0ne]

When dealing with current_RouterConfiguration FULL message_type update, the current code in aca_ovs_l3_programmer.cpp would first destroy any existing router and then create a new one. This has impact on DP causing interruption of existing connections. We want to come up with a plan and algorithm to do careful replacement update.

  if (current_RouterConfiguration.message_type() == MessageType::FULL) {
    // since message_type is full, we can simply remove the existing entry and use
    // the next router entry population block
    overall_rc = delete_router(current_RouterConfiguration, dataplane_programming_time);