When gnrc_rpl_init was called from a thread with higher priority than
the RPL thread, the initializer's call to gnrc_netreg_register would be
executed before the event loop even had a chance to set up its message
queue.
The added short-lived lock makes it work from threads of any priority.
The gnrc_netif_ipv6_addr_add_internal() function unconditionally
acquires the global netif rmutex lock but doesn't release this lock on
this specific path (i.e. if gnrc_netif_ipv6_group_join_internal failed).
This can cause a deadlock as no other thread will afterwards be capable
of acquiring the netif lock.
Non-routing 6LNs do not have to join the solicited nodes address, so
probing for a neighbor using that address may be in vain and only
spamming the LLN with unnecessary messages. RFC 6775 basically assumes
this in section 5.2:
> There is no need to join the solicited-node multicast address, since
> nobody multicasts NSs in this type of network.
Using `gnrc_border_router` with `uhcp` is quite noisy.
uhcpc will regularly refresh the prefix and print a bunch of status messages.
Allow the user to tone it down by setting a higher `LOG_LEVEL`.
For this, convert calls to `printf()` and `puts()` to `LOG_xxx()`.
This requires a dummy header for `uhcpd`.
In accordance with RFC 6775, section 5.2 an NCE should be set STALE
when an ARO renews the address registration for the address:
> The routers SHOULD NOT garbage-collect Registered NCEs (see
> Section 3.4), since they need to retain them until the Registration
> Lifetime expires. Similarly, if NUD on the router determines that
> the host is UNREACHABLE (based on the logic in [RFC4861]), the NCE
> SHOULD NOT be deleted but rather retained until the Registration
> Lifetime expires. A renewed ARO should mark the cache entry as
> STALE. Thus, for 6LoWPAN routers, the Neighbor Cache doesn't behave
> like a cache. Instead, it behaves as a registry of all the host
> addresses that are attached to the router.
xtimer.h must not be included, when the xtimer module is not use. Otherwise
compilation on the waspmote-pro with https://github.com/RIOT-OS/RIOT/pull/14799
will not longer work. gnrc_netif_pktq includes xtimer.h and uses xtimer, but
gnrc_netif includes gnrc_netif_pktq.h regardless of whether gnrc_netif_pktq
is used. This makes sure that gnrc_netif_pktq.h is only included when actually
used.
