BUG/MEDIUM: mux-h1: Don't skip the TCP splicing when there is no more data to read

BUG/MEDIUM: mux-h1: Don't skip the TCP splicing when there is no more data to read

When there is no more data to read (h1m->curr_len == 0 in the state
H1_MSG_DATA), we still call xprt->rcv_pipe() callback. It is important to update
connection's flags. Especially to remove the flag CO_FL_WAIT_ROOM. Otherwise,
the pipe remains marked as full, preventing the stream-interface to fallback on
rcv_buf(). So the connection may be freezed because no more data is received and
the mux H1 remains blocked in the state H1_MSG_DATA.

This patch must be backported to 1.9.