BUG/MEDIUM: mux-h1: Report the right amount of data xferred in h1_rcv_buf()

h1_rcv_buf() must return the amount of data copied in the channel's buffer and
not the number of bytes parsed. Because this value is used during the fast
forwarding to decrement to_forward value, returning the wrong value leads to
undefined behaviours.

This patch must be backported to 1.9.
1 file changed