Fix IPv6 netmask format for sysconfig (#1215)

This change converts the IPv6 netmask from the network_data.json[1]
format to the CIDR style, <IPv6_addr>/<prefix>.

Using an IPv6 address like ffff:ffff:ffff:ffff:: does not work with
NetworkManager, nor networkscripts.

NetworkManager will ignore the route, logging:
  ifcfg-rh: ignoring invalid route at \
    "::/:: via fd00:fd00:fd00:2::fffe dev $DEV" \
    (/etc/sysconfig/network-scripts/route6-$DEV:3): \
    Argument for "::/::" is not ADDR/PREFIX format

Similarly if using networkscripts, ip route fail with error:
  Error: inet6 prefix is expected rather than \
    "fd00:fd00:fd00::/ffff:ffff:ffff:ffff::".

Also a bit of refactoring ...

cloudinit.net.sysconfig.Route.to_string:
* Move a couple of lines around to reduce repeated code.
* if "ADDRESS" not in key -> continute, so that the
  code block following it can be de-indented.
cloudinit.net.network_state:
* Refactors the ipv4_mask_to_net_prefix, ipv6_mask_to_net_prefix
  removes mask_to_net_prefix methods. Utilize ipaddress library to
  do some of the heavy lifting.

LP: #1959148

1 files changed, 3 insertions, 1 deletions

diff --git a/tests/unittests/net/test_init.py b/tests/unittests/net/test_init.py
index b245da94..18b3fe59 100644
--- a/tests/unittests/net/test_init.py
+++ b/tests/unittests/net/test_init.py
@@ -629,7 +629,9 @@ class TestEphemeralIPV4Network(CiTestCase):
                 with net.EphemeralIPv4Network(**params):
                     pass
             error = context_manager.exception
-            self.assertIn("Cannot setup network: netmask", str(error))
+            self.assertIn(
+                "Cannot setup network, invalid prefix or netmask: ", str(error)
+            )
             self.assertEqual(0, m_subp.call_count)
 
     def test_ephemeral_ipv4_network_performs_teardown(self, m_subp):