NetworkManager plugin only supports a single active connection

[tonireed]

System (please complete the following information):

• OS: Debian 12.0
• Kernel version: 6.0.0
• strongSwan version: 5.9.8
• Tested/confirmed with the latest version: yes

Describe the bug
The NetworkManager plugin strongswan only supports a single active connection.

To Reproduce
Steps to reproduce the behavior:

1. Create multiple connections that use the NetworkManager plugin strongswan.
2. Activate the first connection.
3. Try to activate the second connection.

Expected behavior
The NetworkManager plugin strongswan supports a single active connection. The property supports-multiple-connections in the section VPN Connection in the file nm-strongswan-service.name is set to true.

Logs/Backtraces
The following error message should appear in the output of nmcli and in the log of NetworkManager:

The 'strongswan' plugin only supports a single active connection.

Additional context
Manually setting the property supports-multiple-connections in the section VPN Connection in the file nm-strongswan-service.name is set to true does not appear to solve the issue.

[tobiasbrunner]

Manually setting the property supports-multiple-connections in the section VPN Connection in the file nm-strongswan-service.name is set to true does not appear to solve the issue.

Because the plugin doesn't support multiple connections. Would require quite some work to correctly track multiple connections/IKE_SAs in charon-nm.