docs: networking: Fix failover build warnings

Currently building the net_failover docs causes a bunch of warnings to
be emitted.  These warnings are all related to indentation and correctly
highlight missing '::' (for code sections).  It looks, from other rst
files in Documentation, that the first column should be indented 2
spaces.

Add '::' before code snippets and indent all snippets uniformly starting
with 2 spaces.

Cc: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Tobin C. Harding <me@tobin.cc>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/net_failover.rst

@@ -36,6 +36,7 @@ feature on the virtio-net interface and assign the same MAC address to both
 virtio-net and VF interfaces.
 
 Here is an example XML snippet that shows such configuration.
+::
 
   <interface type='network'>
     <mac address='52:54:00:00:12:53'/>
@@ -56,6 +57,7 @@ Here is an example XML snippet that shows such configuration.
 
 Booting a VM with the above configuration will result in the following 3
 netdevs created in the VM.
+::
 
   4: ens10: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
       link/ether 52:54:00:00:12:53 brd ff:ff:ff:ff:ff:ff
@@ -80,6 +82,7 @@ the paravirtual datapath when the VF is unplugged.
 
 Here is a sample script that shows the steps to initiate live migration on
 the source hypervisor.
+::
 
   # cat vf_xml
   <interface type='hostdev' managed='yes'>