This may avoid infinite loops if parameters are being set based on events
sent by parameter changes. It's also what alsa-acp devices do, so bluez5
should follow.
Move SCO polling to a single place, and abstract mtu handling.
Autodetect suitable tx packet size based on rx, instead of relying on
the kernel providing correct values.
Since the data thread accesses the spa_bt_transport, its destroy event
needs to sync with data thread to avoid races.
Also check transport is present in places that need it.
Simplify mSBC buffer handling and syncing to frame headers to work
on a per-byte basis.
The previous code could terminate with buffer overrun if it encountered
multiple consecutive incomplete packets.
Backends don't necessarily allow for opening the same device multiple
times, and it shouldn't be necessary.
Since source and sink are not necessarily both running at the same time,
refcount the transport acquire/release so that it knows to close the fd
only when no source/sink is running.
Let the transport manage the fd lifecycle, also closing it once it is
not needed.
Don't return the fd from acquire(), since each transport is associated
with a single socket fd.
It seems that some BT adapters don't return correct SCO MTU, see
https://marc.info/?t=148586768600002&r=1&w=2
Do not try to autodetect the MTU and use a fix MTU size of 48 bytes.
This is more in line with wayland and it allows us to create new
interfaces in modules without having to add anything to the type
enum. It also removes some lookups to map type_id to readable
name in debug.
