Bluetooth: Host: Log when connecting while scanning may give bad params

The API documentation already states that the controller may require
the scan interval and window used for scanning and connection
establishment to be equal to obtain the best performance.

This commit prints out a warning when this is not the case. The code
size is unchanged when `CONFIG_BT_SCAN_AND_INITIATE_IN_PARALLEL=n`.

This makes application developers aware that using the parameters
`BT_LE_SCAN_ACTIVE_CONTINUOUS` with `BT_CONN_LE_CREATE_CONN` may not
give the best performance.

Signed-off-by: Rubin Gerritsen <rubin.gerritsen@nordicsemi.no>