le_scanning_manager: Fix scannable advertisement event type

The legacy scan response 'connectable' event type bit was
hardcoded to 'true', which was incorrect for ADV_SCAN_IND
advertisements. This change stores the event type of
the original advertising report so that the 'connectable'
bit can be added to the scan response only if necessary
(for ADV_IND).

Bug: 312883465
Bug: 316013235
Test: atest LeScanningManagerTest
Test: atest LeScanningReassemblerTest
Change-Id: If192a9921ea5c93fac46b7532103163e907b7974