Bump the native protocol version

Bump the native protocol version

The previous AAC pass-through patch (commit: 53807e4a) introduced
a new encoding format type: PA_ENCODING_MPEG2_AAC_IEC61937,
which is mostly used in pa_format_info, but forgot to increment the
protocol version number. The version needs to be incremented, because
clients need some way of checking whether the server supports the new
encoding.