python3: enable bluetooth support by default

python3: enable bluetooth support by default

Bluetooth support requires bluez-libs present, but they are only required
for the build, and don't seem to be needed to be present on the target.

There isn't any linking required to libbluetooth. It's only the bluetooth.h
header that is required for building BT support into Python.

For testing, this snippet was used from `Lib/test/test_socket.py` (inside
cpython):
```
def _have_socket_bluetooth():
    """Check whether AF_BLUETOOTH sockets are supported on this host."""
    try:
        # RFCOMM is supported by all platforms with bluetooth support. Windows
        # does not support omitting the protocol.
        s = socket.socket(socket.AF_BLUETOOTH, socket.SOCK_STREAM, socket.BTPROTO_RFCOMM)
    except (AttributeError, OSError):
        return False
    else:
        s.close()
    return True
```

Fixes: https://github.com/openwrt/packages/issues/16544
Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>