MEDIUM: stream-interface: add a snd_buf() callback to sock_ops

This callback is used to send data from the buffer to the socket. It is
the old write_loop() call of the data layer which is used both by the
->write() callback and the ->chk_snd() function. The reason for having
it as a pointer is that it's the only remaining part which causes the
write and chk_snd() functions to be different between raw and ssl.
diff --git a/include/types/stream_interface.h b/include/types/stream_interface.h
index 6fbf94d..e181d57 100644
--- a/include/types/stream_interface.h
+++ b/include/types/stream_interface.h
@@ -117,7 +117,7 @@
 	void (*read)(struct connection *conn);      /* read callback after poll() */
 	void (*write)(struct connection *conn);     /* write callback after poll() */
 	void (*close)(struct connection *);         /* close the data channel on the connection */
-
+	int  (*snd_buf)(struct connection *conn);   /* callback used to send a buffer contents */
 };
 
 /* A stream interface has 3 parts :