It's very unlikely that a pkt snip will have more than 255 users.
Use a uint8_t here to save 4 bytes per snip as this now fits into
the ununsed struct padding.
Router Advertisements are enabled automatically for routing nodes
as soon as they obtain a prefix (e.g. via DHCPv6, UHCP, …).
Enabling router advertisements without a prefix to advertise is
wrong and causes no router solicitations to be send on an upstream
interface.
Also from https://www.rfc-editor.org/rfc/rfc4861#section-6.2.1
Note that AdvSendAdvertisements MUST be FALSE by
default so that a node will not accidentally start
acting as a router unless it is explicitly
configured by system management to send Router
Advertisements.
18477: gnrc_static: add static network configuration r=miri64 a=benpicco
19101: CI: update check-labels-action r=miri64 a=kaspar030
19155: Revert "sys/pm_layered: pm_(un)block add attribute optimize(3)" r=maribu a=Teufelchen1
Revert "sys/pm_layered: pm_(un)block add attribute optimize(3) -shortens hotpath"
This reverts commit 5447203921ab39962d7d378a631a6bc048e7f30b.
### Contribution description
Compiling `examples/gnrc_networking_mac` using `TOOLCHAIN=llvm` yields the following error:
```
RIOT/sys/pm_layered/pm.c:77:16: error: unknown attribute 'optimize' ignored [-Werror,-Wunknown-attributes]
__attribute__((optimize(3)))
```
As indicated, this is because the attribute `optimize` is GCC only and not present in LLVM.
Compare the manpages of [GCC](https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html) and [LLVM](https://clang.llvm.org/docs/AttributeReference.html).
### Testing procedure
Since this should only affect performance and not behavior, no special testing is needed. I am not aware of any tests in RIOT which could verify that assumption.
### Issues/PRs references
Introduced in #18846
There is another instance of this attribute being used in[ shell_lock.c](6fb340d654/sys/shell_lock/shell_lock.c (L80)). Since the usage is security related, I omit it from this PR.
Co-authored-by: Benjamin Valentin <benjamin.valentin@ml-pa.com>
Co-authored-by: Kaspar Schleiser <kaspar@schleiser.de>
Co-authored-by: Teufelchen1 <bennet.blischke@haw-hamburg.de>
