pick better request sequence numbers.  by the way, rand(2) says that
rand returns n s.t. n ≤ 215 when in fact it returns n ≤ 0x7fff.

Notes:
Sun Jul 27 12:20:29 EDT 2008 geoff
    doesn't seem worth it given our existing counter-measures.
    re 215: don't believe nroffed manual pages.


Reference: /n/sources/patch/sorry/dnrand
Date: Sun Jul 27 15:07:23 CES 2008
Signed-off-by: quanstro@quanstro.net
Reviewed-by: geoff

--- /sys/src/cmd/ndb/dnnotify.c	Sun Jul 27 14:04:24 2008
+++ /sys/src/cmd/ndb/dnnotify.c	Sun Jul 27 14:04:22 2008
@@ -56,7 +56,7 @@
 	DNSmsg repmsg;
 
 	/* create the request */
-	reqno = rand();
+	reqno = nrand(0xffff);
 	n = mkreq(soa->owner, Cin, obuf, Fauth | Onotify, reqno);
 
 	/* get an address */
--- /sys/src/cmd/ndb/dnresolve.c	Sun Jul 27 14:04:33 2008
+++ /sys/src/cmd/ndb/dnresolve.c	Sun Jul 27 14:04:30 2008
@@ -1250,7 +1250,7 @@
 //	Dest dest[Maxdest];
 
 	/* pack request into a udp message */
-	req = rand();
+	req = nrand(0xffff);
 	len = mkreq(qp->dp, qp->type, obuf, Frecurse|Oquery, req);
 
 	/* no server addresses yet */