nixos/networkd: add ipv4-fallback and fallback as valid options to LinkLocalAddressing

Both options were introduced in systemd v243[1]. Those options can be
used to ensure that LinkLocalAddressing is only configured for a given
interface if DHCPv4 fails. To quote `systemd.network(5)`:

```
If "fallback" or "ipv4-fallback" is specified, then an IPv4
link-local address is configured only when DHCPv4 fails. If "fallback", an IPv6 link-local
address is always configured, and if "ipv4-fallback", the address is not configured. Note
that, the fallback mechanism works only when DHCPv4 client is enabled, that is, it requires
"DHCP=yes" or "DHCP=ipv4".
```

[1] 8bc17bb3f7
This commit is contained in:
Maximilian Bosch 2019-10-28 20:51:17 +01:00
parent 2d8dc891aa
commit 47724fc77c
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GPG key ID: 091DBF4D1FC46B8E

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@ -187,7 +187,7 @@ let
# Note: For DHCP the values both, none, v4, v6 are deprecated
(assertValueOneOf "DHCP" ["yes" "no" "ipv4" "ipv6" "both" "none" "v4" "v6"])
(assertValueOneOf "DHCPServer" boolValues)
(assertValueOneOf "LinkLocalAddressing" ["yes" "no" "ipv4" "ipv6"])
(assertValueOneOf "LinkLocalAddressing" ["yes" "no" "ipv4" "ipv6" "ipv4-fallback" "fallback"])
(assertValueOneOf "IPv4LLRoute" boolValues)
(assertValueOneOf "LLMNR" ["yes" "resolve" "no"])
(assertValueOneOf "MulticastDNS" ["yes" "resolve" "no"])