slirp: Fix memory leak on small incoming ipv4 packet

Signed-off-by: NSamuel Thibault <samuel.thibault@ens-lyon.org>
Reviewed-by: NThomas Huth <thuth@redhat.com>

slirp/ip_input.c

@@ -85,7 +85,7 @@ ip_input(struct mbuf *m)
 	DEBUG_ARG("m_len = %d", m->m_len);
 
 	if (m->m_len < sizeof (struct ip)) {
-		return;
+		goto bad;
 	}
 
 	ip = mtod(m, struct ip *);