Replace all post_url with Hugo ref blocks

content/articles/2021-09-02-vpp-5.md

@@ -30,11 +30,11 @@ prefixes and 870K IPv4 prefixes.
 ## My test setup
 
 The goal of this post is to show what code needed to be written to extend the **Netlink Listener**
-plugin I wrote in the [fourth post]({% post_url 2021-08-25-vpp-4 %}), so that it can consume
+plugin I wrote in the [fourth post]({{< ref "2021-08-25-vpp-4" >}}), so that it can consume
 route additions/deletions, a thing that is common in dynamic routing protocols such as OSPF and
 BGP.
 
-The setup from my [third post]({% post_url 2021-08-15-vpp-3 %}) is still there, but it's no longer
+The setup from my [third post]({{< ref "2021-08-15-vpp-3" >}}) is still there, but it's no longer
 a focal point for me. I use it (the regular interface + subints and the BondEthernet + subints)
 just to ensure my new code doesn't have a regression.
 
@@ -54,7 +54,7 @@ The test setup offers me the ability to consume OSPF, OSPFv3 and BGP.
 
 ### Startingpoint
 
-Based on the state of the plugin after the [fourth post]({% post_url 2021-08-25-vpp-4 %}),
+Based on the state of the plugin after the [fourth post]({{< ref "2021-08-25-vpp-4" >}}),
 operators can create VLANs (including .1q, .1ad, QinQ and QinAD subinterfaces) directly in
 Linux. They can change link attributes (like set admin state 'up' or 'down', or change
 the MTU on a link), they can add/remove IP addresses, and the system will add/remove IPv4
@@ -163,7 +163,7 @@ compare it to issuing `ip link` and acting on additions/removals as they occur.
 called _direct_, generates directly connected routes for interfaces that have IPv4 or IPv6
 addresses configured. It turns out that if I add `194.1.163.86/27` as an IPv4 address on
 an interface, it'll generate several Netlink messages: one for the `RTM_NEWADDR` which
-I discussed in my [fourth post]({% post_url 2021-08-25-vpp-4 %}), and also a `RTM_NEWROUTE`
+I discussed in my [fourth post]({{< ref "2021-08-25-vpp-4" >}}), and also a `RTM_NEWROUTE`
 for the connected `194.1.163.64/27` in this case. It helps the kernel understand that if
 we want to send a packet to a host in that prefix, we should not send it to the default
 gateway, but rather to a nexthop of the device. Those are intermittently called `direct`