slirp seems to be part of vde2. In the COPYING.slirpvde the license of slirp is
stated. It is copyright Danny Gasparovski and the license includes the
following clause:

3. All advertising materials mentioning features or use of this software
   must display the following acknowledgment:
   This product includes software developed by Danny Gasparovski.

In the subdirectory which contains the slirp there are many files which are
licensed under the more permissive BSD 3 clause license (i.e. the one without
the advertising clause) and under the MIT license (typically those files
written by Fabrice Bellard). However, there are still numerous files there
which contain this notice:

/*
 * Copyright (c) 1995 Danny Gasparovski
 *
 * Please read the file COPYRIGHT for the
 * terms and conditions of the copyright.
 */

A reasonable interpretation of this notice, even in the absence of a COPYRIGHT
file in the immediate directory is that the Danny Gasparovski license with the
advertising clause is meant. This is not compatible with any version of the
GPL.

Thus, if slirp is linked with the rest of the files/components (some being GPL)
an issue of GPL compatibility could arise.

Could you therefore confirm first of all whether slirp is used at all. If it is
used, we will need to check on whether upstream had permission to relicense
files from Danny Gasparovski. If not, we will need to examine the nature of the
interaction of the (c) Danny Gasparovski files with the rest of the package.