Bluetooth: hci_conn: Fix connection cleanup with BIG with 2 or more BIS

Bluetooth: hci_conn: Fix connection cleanup with BIG with 2 or more BIS

This fixes bis_cleanup not considering connections in BT_OPEN state
before attempting to remove the BIG causing the following error:

btproxy[20110]: < HCI Command: LE Terminate Broadcast Isochronous Group (0x08|0x006a) plen 2
        BIG Handle: 0x01
        Reason: Connection Terminated By Local Host (0x16)
> HCI Event: Command Status (0x0f) plen 4
      LE Terminate Broadcast Isochronous Group (0x08|0x006a) ncmd 1
        Status: Unknown Advertising Identifier (0x42)

Fixes: fa224d0c094a ("Bluetooth: ISO: Reassociate a socket with an active BIS")
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>