Fill entry['gateway'] for default IPv6 routes

[andgein]

Fill entry['gateway'] for default IPv6 routes

Otherwise this code (https://github.com/canonical/cloud-init/blob/main/cloudinit/netinfo.py#L478) fails with

failed run of stage init                                                                                     
------------------------------------------------------------                         
Traceback (most recent call last):                                                                           
  File "/usr/lib/python3/dist-packages/cloudinit/cmd/main.py", line 652, in status_wrapper
    ret = functor(name, args)                                                                                
  File "/usr/lib/python3/dist-packages/cloudinit/cmd/main.py", line 283, in main_init                        
    sys.stderr.write("%s\n" % (netinfo.debug_info()))                                                                                                                                                                      
  File "/usr/lib/python3/dist-packages/cloudinit/netinfo.py", line 496, in debug_info                        
    route_lines = route_pformat().splitlines()                                                               
  File "/usr/lib/python3/dist-packages/cloudinit/netinfo.py", line 480, in route_pformat                     
    r['gateway'], r['iface'], r['flags']])                                                                   
KeyError: 'gateway'                                                                                                                                                                                                        
------------------------------------------------------------   

Test Steps

1. Create machine with custom default IPv6 route, i.e.

root@host:~# ip -o -6 route list table all
...                   
default dev eth1 proto static metric 50 pref medium 
...

2. Run cloud-init init

Checklist:

• My code follows the process laid out in the documentation
• I have updated or added any unit tests accordingly
• I have updated or added any documentation accordingly

[andgein]

CLA signing pull request: #1042

[TheRealFalcon]

@andgein , thanks for this.

Additionally, can you add a unit test at the end of test_netinfo.py? The last three tests are dealing with route_pformat, so hopefully it shouldn't be too hard to use them as examples for an additional test.

Also, just for context, this issue has come up before but never got over the finish line: #746 . Feel free to take any suggestions mentioned there, but personally, I don't think they are necessary because:

1. We default ipv4 gateway to 0.0.0.0 even if it's not specified
2. Other tools like route will print :: as the default gateway if not specified and don't seem to have a problem with it.

[github-actions]

Hello! Thank you for this proposed change to cloud-init. This pull request is now marked as stale as it has not seen any activity in 14 days. If no activity occurs within the next 7 days, this pull request will automatically close.

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