sync icmp from nix -> 9 kernels.

Reference: /n/atom/patch/applied/sync9icmp
Date: Sun Jun  7 20:49:19 CES 2015
Signed-off-by: quanstro@quanstro.net

--- /sys/src/9/ip/icmp.c	Sun Jun  7 20:49:10 2015
+++ /sys/src/9/ip/icmp.c	Sun Jun  7 20:49:11 2015
@@ -130,11 +130,10 @@
 icmpstate(Conv *c, char *state, int n)
 {
 	USED(c);
-	return snprint(state, n, "%s qin %d qout %d ttl %d\n",
+	return snprint(state, n, "%s qin %d qout %d\n",
 		"Datagram",
 		c->rq ? qlen(c->rq) : 0,
-		c->wq ? qlen(c->wq) : 0,
-		c->ttl
+		c->wq ? qlen(c->wq) : 0
 	);
 }
 
@@ -319,6 +318,16 @@
 [3]	"port unreachable",
 [4]	"fragmentation needed and DF set",
 [5]	"source route failed",
+[6]	"destination network unknown",
+[7]	"destination host unknown",
+[8]	"source host isolated",
+[9]	"network administratively prohibited",
+[10]	"host administratively prohibited",
+[11]	"network unreachable for tos",
+[12]	"host unreachable for tos",
+[13]	"communication administratively prohibited",
+[14]	"host precedence violation",
+[15]	"precedence cutoff in effect",
 };
 
 static void
@@ -372,8 +381,11 @@
 		ipoput4(icmp->f, r, 0, MAXTTL, DFLTTOS, nil);
 		break;
 	case Unreachable:
-		if(p->code > 5)
-			msg = unreachcode[1];
+		if(p->code >= nelem(unreachcode)){
+			snprint(m2, sizeof m2, "unreachable %V->%V code %d",
+				p->src, p->dst, p->code);
+			msg = m2;
+		}
 		else
 			msg = unreachcode[p->code];
 
@@ -394,7 +406,7 @@
 		break;
 	case TimeExceed:
 		if(p->code == 0){
-			sprint(m2, "ttl exceeded at %V", p->src);
+			snprint(m2, sizeof m2, "ttl exceeded at %V", p->src);
 
 			bp->rp += ICMP_IPSIZE+ICMP_HDRSIZE;
 			if(blocklen(bp) < MinAdvise){