Bluetooth: Allow ACL packets over USB in HCI_RAW mode

Removed tests which prevent transmission of ACL packets
when the device is in HCI_RAW mode. These tests verified that
there are ACL or LE links currently tracked by the HCI
connection manager. However, a HCI_RAW mode device does not
use the connection manager. In these circumstances, the connection
counts will be zero, and thus, transmitted ACL packets dropped.

The acl_num test is actually a vestige of a previous bulk URB
scheme that is no longer used by this driver (bulk URBs were not
started until at least one ACL connection was created). This was
incompatible with some endpoint implementations and was dropped -
see commit 43c2e57f.

The utility of these tests is marginal - currently, the hci tx
scheduler cannot send an ACL or LE packet for an untracked connection
(except if the device is in HCI_RAW mode).

Lastly, no other transport layer driver enforces these same tests.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Acked-by: Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>