MEDIUM: log: add a new LW_XPRT flag to pin the transport layer

This flag will have to be set on log tags which require transport layer
information. They will prevent the conn_xprt_close() call from releasing
the transport layer too early.
diff --git a/include/types/log.h b/include/types/log.h
index 0224326..70dc9fa 100644
--- a/include/types/log.h
+++ b/include/types/log.h
@@ -131,6 +131,7 @@
 #define LW_RSPHDR	2048	/* response header(s) */
 #define LW_BCKIP	4096	/* backend IP */
 #define LW_FRTIP 	8192	/* frontend IP */
+#define LW_XPRT		16384	/* transport layer information (eg: SSL) */
 
 struct logsrv {
 	struct list list;