MINOR: mux-h2: Set HTX extra value when possible

For now, this can be only done when a content-length is specified. In fact, it
is the same value than h2s->body_len, the remaining body length according to
content-length. Setting this field allows the fast forwarding at the channel
layer, improving significantly data transfer for big objects.

This patch may be backported to 1.9.
1 file changed