Bluetooth: Add default connection parameters before pairing

When trying to pair a new Bluetooth Low Energy device, then make sure
that the default connections parameters are in place before trying to
establish the first connection to that device. With the connection
parameters structure allocated, the slave preferred values can now
easily be tracked and all future connections will use the correct
values from that start decreasing connection establishment time.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>