net: decode Bluetooth protocol names unconditionally

net: decode Bluetooth protocol names unconditionally

As we have all BTPROTO_* constant definitions now, there is no need
to rely on bluetooth.h header anymore.

* net.c (AF_BLUETOOTH): Provide a fallback definition.
[HAVE_BLUETOOTH_BLUETOOTH_H]: Do not include <bluetooth/bluetooth.h>.
[!HAVE_BLUETOOTH_BLUETOOTH_H]: Include "xlat/bt_protocols.h".
[!HAVE_BLUETOOTH_BLUETOOTH_H] (decode_sockbuf): Decode AF_BLUETOOTH.
(decode_sockbuf) <case AF_BLUETOOTH>: Use printxval_index.
* xlat/bt_protocols.in: Add "#value_indexed" directive.