This seems to be a problem related to local and remote IDs of the Ipsec configuration.
Because the Vodafone Station doesn’t allow you to specify the IDs I assume that it’s using Public IPs as identifiers.
So, if your Nethserver has a public ip on the red interface yuo can set local and remote id that way:
local ID: public ip adress of nethserver
remote ID: public ip adress of the vodafone station