BUG/MINOR: mux-h1: Don't rely on CO_FL_SOCK_RD_SH to set H1C_F_CS_SHUTDOWN

BUG/MINOR: mux-h1: Don't rely on CO_FL_SOCK_RD_SH to set H1C_F_CS_SHUTDOWN

The CO_FL_SOCK_RD_SH flag is only set when a read0 is received. So we must not
rely on it to set the H1 connection in shutdown state (H1C_F_CS_SHUTDOWN). In
fact, it is suffisant to set the connection in shutdown state when the shutdown
for writes is forwared to the sock layer.

This patch must be backported as far as 1.9.

(cherry picked from commit 7b109f2f8b9cb493d9f6c01f1613bc54a6f71ba3)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>