Don't send stuff to blacklisted nodes.

The internal blacklist was only used on reception, which is okay
since it's supposed to trigger very seldom.  If we're ever going
to use it for other purposes, we should make it more general.

dht.c

@@ -1364,10 +1364,8 @@ node_blacklisted(const struct sockaddr *sa, int salen)
 {
     int i;
 
-    if(salen > sizeof(struct sockaddr_storage)) {
-        debugf("Checking for overlong blacklisted node.\n");
-        return -1;
-    }
+    if(salen > sizeof(struct sockaddr_storage))
+        abort();
 
     for(i = 0; i < DHT_MAX_BLACKLISTED; i++) {
         if(memcmp(&blacklist[i], sa, salen) == 0)
@@ -2312,6 +2310,12 @@ dht_send(const void *buf, size_t len, int flags,
     if(salen == 0)
         abort();
 
+    if(node_blacklisted(sa, salen)) {
+        debugf("Attempting to send to blacklisted node.\n");
+        errno = EPERM;
+        return -1;
+    }
+
     if(sa->sa_family == AF_INET)
         s = dht_socket;
     else if(sa->sa_family == AF_INET6)