Bluetooth: hci_conn: Consolidate code for aborting connections

This consolidates code for aborting connections using
hci_cmd_sync_queue so it is synchronized with other threads, but
because of the fact that some commands may block the cmd_sync_queue
while waiting specific events this attempt to cancel those requests by
using hci_cmd_sync_cancel.

Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>