Bluetooh: Host: conn: Resume adv after disconn for periph role only

Zephyrs Host has by default enabled automatic resume of advertising
in case of disconnection when peripheral role is enabled.

The feature becomes a bit problematic in case of multirole usage.
For example assume a use case where a device is working as peripheral
and central, where it may establish single connection for each role.

In case there are two connections established and connection in
central role is dropped by peer, Host will automatically resume
advertising. After that an application can resume scanning, e.g.
in disconnected callback. That should not happen.

If one of connections was used for central role, it should not
be stolen by Host to run peripheral role. Host should verify
if a disconnected connection role was peripheral and then resume
advertising.

This approach will not break backward compatibility and change
correct resume behavior. What more, Host will follow an application
decisions about use of connection objects.

Signed-off-by: Piotr Pryga <piotr.pryga@nordicsemi.no>