REDHAT-BUG-2565425: Medium severity vulnerability

A flaw was found in libslirp in ifoutput() in src/if.c. When demoting an interactive session from the fast queue to the batch queue after throughput limits were exceeded, the code called slirpremque() and slirpinsque() on ifm->mnextpkt (an arbitrary packet in the circular session list) instead of the session queue head. This corrupted doubly-linked queue pointers. Subsequent traversals in ifstart() could crash the host process that embeds libslirp (for example QEMU or slirp4netns), resulting in a guest-to-host denial of service.