kernel-netlink: Actually verify if the netlink message exceeds the buffer size

It might equal it and that's fine. With MSG_TRUNC we get the actual
message size and can only report an error if we haven't received the
complete message.

src/libhydra/plugins/kernel_netlink/kernel_netlink_shared.c

@@ -185,8 +185,8 @@ static ssize_t read_msg(private_netlink_socket_t *this,
 			return -1;
 		}
 	}
-	len = recv(this->socket, buf, buflen, block ? 0 : MSG_DONTWAIT);
-	if (len == buflen)
+	len = recv(this->socket, buf, buflen, MSG_TRUNC|(block ? 0 : MSG_DONTWAIT));
+	if (len > buflen)
 	{
 		DBG1(DBG_KNL, "netlink response exceeds buffer size");
 		return 0;