config.h needs to be consistently included before any standard headers
if we ever want to set feature test macros (like _GNU_SOURCE or whatever)
inside. It can lead to hard-to-debug issues without that.
It can also be problematic just for our own HAVE_* that it may define
if it's not consistently made available before our own headers. Just
always include it first, before everything.
We already did this in many files, just not consistently.
Similarly as in spa_dbus, don't exit if bus goes down. Neither the
audio or midi Bluetooth backend reconnects to DBus, but they shouldn't
exit the process.
Use stdalign.h instead of union.
Fix some refcounting and return values.
Fail early in add_filters.
Minor style cleanups.
Less magical spa_dbus_async_call.
As server, put node nick in GATT Characteristic User Description, so
that clients have some information which endpoint is which in case we
have multiple. This is not in BLE MIDI standard, but cannot hurt.
As client, make use of that information, if present.
