Bluetooth: Host: Reassemble extended advertising reports

The host reassembles fragmented advertising reports from the controller.

Non-complete advertising reports from different advertisers may not be
interleaved. If non-complete advertising reports from an advertiser
is received while advertising reports from another advertiser is
reassembled, an error message is logged and the advertising report is
discarded. Future scan results may be incomplete.

Advertising reports from legacy PDUs or complete extended advertising
reports may be interleaved as these do not require reassembly.

If the controller sends more advertising data than fits in the
reassembly buffer, the data is truncated. Further advertising reports
from the advertiser are discarded until the final complete advertising
report is received and discarded.

Signed-off-by: Herman Berget <herman.berget@nordicsemi.no>