Core Update 196: Adjust existing IPsec connections using ML-KEM

Core Update 196: Adjust existing IPsec connections using ML-KEM

This causes existing IPsec connections using ML-KEM to always use it in
conjunction with Curve 25519, in line with the changes dfa7cd2bbac3c746569368d70fefaf1ff4e1fed2
implements for newly configured IPsec connections.

Again, we can reasonably assume an IPsec peer supporting ML-KEM also
supports Curve 25519. In case such a peer does not support RFC 9370, and
the IPsec connection was created using our default ciphers, it will fall
back to Curve 448, Curve 25519, or any other traditional algorithm.

This patch will break existing IPsec connections only if they are
exclusively using ML-KEM (which means the IPFire user reconfigured them
manually using the "advanced connection settings" section in the WebUI),
and the IPsec peer is configured in the same manner, and/or is an IPFire
machine not yet updated to Core Update 196. Any other IPFire-to-IPFire
IPsec connection will continue working, potentially falling back to
Curve 448 or 25519 until both peers are updated to Core Update 196,
after which ML-KEM in conjunction with Curve 25519 will be used again.

The second version of this patch modifies IPFire's own configuration
file for IPsec connections, rather than applying these changes directly
to /etc/ipsec.conf, where they would have been overwritten by the next
WebUI change.

Signed-off-by: Peter Müller <peter.mueller@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>