Bluetooth: Validate input parameters of gatt characteristics

If the input parameters of gatt characteristics are not valid
return false

Change-Id: Icf44439992cb068339f7a4c4e50a3f28c25db6ce
CRs-Fixed: 534763
Bluetooth: Fix PXP LPP app link loss reconnection

When BLE link loss reconnection happens,the host is
not able to send Vendor specific commands
to the controller to start monitoring the RSSI
values.

CRs-fixed: 597822

Change-Id: I436889fae7f7d42c4f532690b726271ffc136e94