MINOR: quic: use real sending rate measurement

Before this patch, global sending rate was measured on the QUIC lower
layer just after sendto(). This meant that all QUIC frames were
accounted for, including non STREAM frames and also retransmission.

To have a better reflection of the application data transferred, move
the incrementation into the MUX layer. This allows to account only for
STREAM frames payload on their first emission.

This should be backported up to 2.6.
2 files changed