fixup! gnrc_sixlowpan_iphc: add rudimentary forwarding routine

sys/net/gnrc/network_layer/sixlowpan/iphc/gnrc_sixlowpan_iphc.c

@@ -853,7 +853,12 @@ void gnrc_sixlowpan_iphc_recv(gnrc_pktsnip_t *sixlo, void *rbuf_ptr,
                 }
             }
             if ((ipv6 == NULL) || (res < 0)) {
-                /* TODO fall-back to reassembly in minfwd when ipv6 != NULL */
+                /* TODO: There is a potential to fall-back to classic reassembly
+                 * when ipv6 != NULL. However, since `ipv6` was reversed in
+                 * `_encode_frag_for_forwarding`, that step needs to be reversed
+                 * or a version of the old ipv6 needs to be held in the buffer.
+                 * For now, just drop the packet all together in an error case
+                 */
                 gnrc_sixlowpan_frag_vrb_rm(vrbe);
             }
             gnrc_pktbuf_release(sixlo);