Free DHCP options with length zero.

Otherwise they are leaked, allowing an attacker to trigger memory
exhaustion.

This is options.c rev. 1.70 from OpenBSD.

admbugs:	552
Obtained from:	OpenBSD
MFC after:	3 days

sbin/dhclient/options.c

@@ -896,6 +896,5 @@ do_packet(struct interface_info *interface, struct dhcp_packet *packet,
 
 	/* Free the data associated with the options. */
 	for (i = 0; i < 256; i++)
-		if (tp.options[i].len && tp.options[i].data)
-			free(tp.options[i].data);
+		free(tp.options[i].data);
 }