MINOR: quic: account Tx data per stream

MINOR: quic: account Tx data per stream

Add accounting at qc_stream_desc level to be able to report the number
of allocated Tx buffers and the sum of their data. This represents data
ready for emission or already emitted and waiting on ACK.

To simplify this accounting, a new counter type bdata_ctr is defined in
quic_utils.h. This regroups both buffers and data counter, plus a
maximum on the buffer value.

These values are now displayed on QCS info used both on logline and
traces, and also on "show quic" output.