Fix MCT data transport for the BT HAL

The vendor open interface command returns the total number
of FDs opened. (2 or 4 if the interface is MCT)

However, the list of FDs is always 4 in either case. If the
open command returns 2, the FDs are shared cmd/event and
data in/out.

2 FDs example
[41, 41, 42, 42]

4 FDs example
[41, 42, 43, 44]

If we condition the registration of ACL_IN on the total
number of FDs, then 2 FD MCT interfaces will not get data.

Fixes: 36067612, 36035039, 36188793
Test: manual, pairing is quick and data does transfer
Change-Id: Icc8728239ba81426d5fc0e678c5c5480fd9b5081