[strongSwan] disregarded diffie hellmann group

[Marco Berizzi]

> [1] https://wiki.strongswan.org/projects/strongswan/wiki/ExpiryRekey#IKEv2

Thanks for the hints, Tobias.
I have patched the configuration like this:

from esp_proposals = aes256-sha512-ecp521
to esp_proposals = aes256-sha512-ecp521,aes256-sha512

Marco