Update logic for forwardedForHeadersWorking

As discussed in https://github.com/nextcloud/server/issues/11594

 when discovering if
x-forwarded-for is working properly its not possible to use getRemoteAddr because
the "client ip" is returned. For this check the ip of the last hop would be required.

Signed-off-by: Daniel Kesselberg <mail@danielkesselberg.de>