sae: Fix potential leak in sae_process_anti_clogging

We may receive multiple anti-clogging request messages.  We memdup the
token every time, without checking whether memory for one has already
been allocated.  Free the old token prior to allocating a new one.

src/sae.c

@@ -898,6 +898,7 @@ static int sae_process_anti_clogging(struct sae_sm *sm, const uint8_t *ptr,
 		return -EBADMSG;
 	}
 
+	l_free(sm->token);
 	sm->token = l_memdup(ptr, len);
 	sm->token_len = len;
 	sm->sync = 0;