vif: T3349: use fixed ordering when enabling parent and child interface

When a VIF/VLAN interface is placed in admin down state but the lower
interface, serving the vlan, is moved from admin down -> admin up, all its
vlan interfaces will be placed in admin up state, too.

This is bad as a VLAN interface will become admin up even if its specified as
admin down after a reboot.

To reproduce:
  set interfaces ethernet eth1 vif 20 disable
  set interfaces ethernet eth1 disable
  commit

  delete interfaces ethernet eth1 disable
  commit

Now check the interface state and it returns UP,LOWER_UP
7: eth1.20@eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 00:50:56:b3:09:07 brd ff:ff:ff:ff:ff:ff
    inet6 fe80::250:56ff:feb3:907/64 scope link
       valid_lft forever preferred_lft forever

1 files changed, 0 insertions, 19 deletions

diff --git a/python/vyos/ifconfig/dummy.py b/python/vyos/ifconfig/dummy.py
index 0019fc52b..d45769931 100644
--- a/python/vyos/ifconfig/dummy.py
+++ b/python/vyos/ifconfig/dummy.py
@@ -31,22 +31,3 @@ class DummyIf(Interface):
             'prefixes': ['dum', ],
         },
     }
-
-    def update(self, config):
-        """ General helper function which works on a dictionary retrived by
-        get_config_dict(). It's main intention is to consolidate the scattered
-        interface setup code and provide a single point of entry when workin
-        on any interface. """
-
-        # call base class first
-        super().update(config)
-
-        # Enable/Disable of an interface must always be done at the end of the
-        # derived class to make use of the ref-counting set_admin_state()
-        # function. We will only enable the interface if 'up' was called as
-        # often as 'down'. This is required by some interface implementations
-        # as certain parameters can only be changed when the interface is
-        # in admin-down state. This ensures the link does not flap during
-        # reconfiguration.
-        state = 'down' if 'disable' in config else 'up'
-        self.set_admin_state(state)