Make dg_echo return up to the first 65536 bytes of a datagram.

The patch I used isn't quite the one Lars suggested, but the size
of the largest datagram you can recv isn't #defined anywhere, and
probably isn't even bounded for some protocols.

PR:		25050
Submitted by:	Lars Eggert <larse@isi.edu>

usr.sbin/inetd/builtins.c

@@ -267,7 +267,7 @@ echo_dg(s, sep)			/* Echo service -- echo data back */
 	int s;
 	struct servtab *sep;
 {
-	char buffer[BUFSIZE];
+	char buffer[65536]; /* Should be sizeof(max datagram). */
 	int i;
 	socklen_t size;
 	struct sockaddr_storage ss;