ringaccount: don't export DHT port to archive

Multiple accounts won't be able to register if
they use the same DHT port.
Prevent multiple accounts to use the same DHT port
by avoiding to include the DHT port configuration
in the account archive.
This will force Ring to use a new random port on device creation
from the archive.

Change-Id: If5b2143b731aba38d7ee0f921510c55d8289bdd3
Reviewed-by: Andreas Traczyk <andreas.traczyk@savoirfairelinux.com>