[PATCH proxmox] fix #7723: network-api: avoid overwriting existing inet6 family method

[Shan Shaji <s.shaji@proxmox.com>]

If the inet6 address family's cidr6/gatway6 values are not present, the
interface.method6 values is mutated with `NetworkConfigMethod::Manual`
even if the interface.method6 already has a value. For example, if
the config method is `auto` then it gets replaced by `Manual` config
method.

Later, when writing the config file to the interfaces.new file if the
config method is manual and if there are no IPv6 specific attributes
present, then the inet6 stanza gets skipped.

In order to fix the issue update the condition to only set the config
method to `::Manual` if there is no value present inside the `method6`
property of the interface object.

Signed-off-by: Shan Shaji <s.shaji@proxmox.com>
---

 note: The issue where the UI showed an error has already been fixed
 in commit (#973cf333). 
 
 proxmox-network-api/src/api_impl.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/proxmox-network-api/src/api_impl.rs b/proxmox-network-api/src/api_impl.rs
index 9d956e2c..ee78a88c 100644
--- a/proxmox-network-api/src/api_impl.rs
+++ b/proxmox-network-api/src/api_impl.rs
@@ -332,7 +332,7 @@ pub fn update_interface(
 
     if interface.cidr6.is_some() || interface.gateway6.is_some() {
         interface.method6 = Some(NetworkConfigMethod::Static);
-    } else {
+    } else if interface.method6.is_none() {
         interface.method6 = Some(NetworkConfigMethod::Manual);
     }
 
-- 
2.47.3