Bluetooth: Controller: Fix continuous scan initiator from being aborted

Fix to prevent a transmitted CONNECT_REQ PDU from being
aborted mid-air when initiator is using continuous scan
window that do not use time reservation. A different state
or role that overlaps the connection initiation requesting
for an abort should be denied when CONNECT_REQ PDU has been
enqueued for tranmission by the radio.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>