Bluetooth: hci: df: Fix unnecessary IQ sample storage

In case Controller reports to Host insufficient resources to store IQ
samples, according to BT 5.3 Core spec. Vol 4, Part E, sections
7.7.65.21 and 7.7.65.22:
1) packet_status shall be set to BT_HCI_LE_CTE_INSUFFICIENT_RESOURCES
2) sample_count shall be set to zero.
That means there should be no IQ samples stored in IQ report.

HCI implementation stored single IQ sample with value BT_HCI_LE_CTE-
_REPORT_NO_VALID_SAMPLE.

The commit fixes that. No additional memory is added to event buffer
and no IQ sample is stored if sample_count is zero.

Also there is added code that handles situation where ULL provides
IQ report with packet_status indicating valid IQ samples report
but sample_count is zero. In such case Host event stores single IQ
sample with value BT_HCI_LE_CTE_REPORT_NO_VALID_SAMPLE.
In case of vendor specific counter part of the event the value is
BT_HCI_VS_LE_CTE_REPORT_NO_VALID_SAMPLE.

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