MINOR: stream/mux: implement websocket stream flag

Define a new stream flag SF_WEBSOCKET and a new cs flag CS_FL_WEBSOCKET.
The conn-stream flag is first set by h1/h2 muxes if the request is a
valid websocket upgrade. The flag is then converted to SF_WEBSOCKET on
the stream creation.

This will be useful to properly manage websocket streams in
connect_server().

include/haproxy/connection-t.h

@@ -86,6 +86,9 @@ enum {
 	 * the stream-interface :
 	 */
 	CS_FL_NOT_FIRST     = 0x00100000,  /* this stream is not the first one */
+
+	/* flags set by the mux relayed to the stream */
+	CS_FL_WEBSOCKET     = 0x00200000,  /* websocket stream */
 };
 
 /* cs_shutr() modes */

include/haproxy/stream-t.h

@@ -80,6 +80,7 @@
 
 #define SF_SRV_REUSED   0x00100000	/* the server-side connection was reused */
 #define SF_SRV_REUSED_ANTICIPATED  0x00200000  /* the connection was reused but the mux is not ready yet */
+#define SF_WEBSOCKET    0x00400000	/* websocket stream */
 
 /* flags for the proxy of the master CLI */
 /* 0x1.. to 0x3 are reserved for ACCESS_LVL_MASK */