Update docs for ReqStart in vsl(7), adding the listener name field.

include/tbl/vsl_tags.h

@@ -269,13 +269,14 @@ SLTM(VCL_return, 0, "VCL method return value",
 )
 
 SLTM(ReqStart, 0, "Client request start",
-	"Start of request processing. Logs the client IP address and port"
-	" number.\n\n"
+	"Start of request processing. Logs the client address, port number "
+	" and listener endpoint name (from the -a command-line argument).\n\n"
 	"The format is::\n\n"
-	"\t%s %s\n"
-	"\t|  |\n"
-	"\t|  +- Client Port number\n"
-	"\t+---- Client IP4/6 address\n"
+	"\t%s %s %s\n"
+	"\t|  |  |\n"
+	"\t|  |  +-- Listener name (from -a)\n"
+	"\t|  +----- Client Port number (0 for Unix domain sockets)\n"
+	"\t+-------- Client IP4/6 address (0.0.0.0 for UDS)\n"
 	"\n"
 )