don't get confused by ifcs created by the clone device but
with no associated device.  also don't corrupt memory
if parsing goes wrong.

example:
minooka; cat /net/ipifc/1/status
device  maxtu 0 sendra 0 recvra 0 mflag 0 oflag 0 maxraint 0 minraint 0 linkmtu 0 reachtime 0 rxmitra 0 ttl 0 routerlt 0 pktin 0 pktout 0 errin 0 errout 0
minooka; ipifc
0:/net/ether0 	00304861c89e	1514
	205.185.197.113/120	205.185.197.0
1:maxtu 	0
0:/net.alt/ether1 	00304861c89f	1514
	65.14.39.134/123	65.14.39.128
	12.51.113.6/123	12.51.113.0
0:/net.10g/ether4 	0060dd4785f5	9000
	205.185.197.114/120	205.185.197.0
minooka; 8.ipifc	# compiled with change.
0:/net/ether0 	00304861c89e	1514
	205.185.197.113/120	205.185.197.0
0:/net.alt/ether1 	00304861c89f	1514
	65.14.39.134/123	65.14.39.128
	12.51.113.6/123	12.51.113.0
0:/net.10g/ether4 	0060dd4785f5	9000
	205.185.197.114/120	205.185.197.0

Reference: /n/sources/patch/applied/readipifc
Date: Tue Jan 29 16:54:07 CET 2008
Signed-off-by: quanstro@quanstro.net

--- /sys/src/libip/readipifc.c	Tue Jan 29 16:48:37 2008
+++ /sys/src/libip/readipifc.c	Tue Jan 29 16:48:35 2008
@@ -61,7 +61,7 @@
 	char buf[4*1024];
 	char *line[32];
 	char *f[64];
-	Ipifc *ifc;
+	Ipifc *ifc, **l0;
 	Iplifc *lifc, **ll;
 
 	/* read the file */
@@ -76,11 +76,14 @@
 
 	if(strncmp(buf, "device", 6) != 0)
 		return _readoldipifc(buf, l, index);
-
+	/* ignore ifcs with no associated device */
+	if(strncmp(buf+6, "  ", 2) == 0)
+		return l;
 	/* allocate new interface */
 	*l = ifc = mallocz(sizeof(Ipifc), 1);
 	if(ifc == nil)
 		return l;
+	l0 = l;
 	l = &ifc->next;
 	ifc->index = index;
 
@@ -88,10 +91,14 @@
 
 	/* pick off device specific info(first line) */
 	n = tokenize(line[0], f, nelem(f));
+	if(n%2)
+		goto lose;
 	strncpy(ifc->dev, findfield("device", f, n), sizeof(ifc->dev));
 	ifc->dev[sizeof(ifc->dev)-1] = 0;
 	if(ifc->dev[0] == 0){
+lose:
 		free(ifc);
+		*l0 = nil;
 		return l;
 	}
 	ifc->mtu = strtoul(findfield("maxtu", f, n), nil, 10);