The API and internals forced a single, activated IP2IP account.
This design prevented to disable the IP2IP account or to have multiple
IP2IP accounts (eg. on different ports, IPv4 and IPv6 etc.)

This patch completly removes the "IP2IP" account concept from the daemon.
An SIP account is now considered "IP2IP" if it has no hostname.

Change-Id: I483dbbb9e5546f7c54fbf2d2910a93200ef3b82c
Tuleap: #448
Signed-off-by: Guillaume Roguez <guillaume.roguez@savoirfairelinux.com>