gnrc_ipv6_nib: fix preparation of delayed NA

tests/periph_eeprom: use EEPROM_CLEAR_BYTE

gnrc_ipv6_nib/arsm: ensure proper int width in backoff calculation

dist/tools: Add script for backporting PR's

This was primarily done so the backoff can be tested

Otherwise, the result might flow over on 8/16-bit platforms

After being cleared, the memory can be `0xFF` for `atmega` platforms for
example.

Fix the test to take EEPROM_CLEAR_BYTE into account.

`strcmp` was used to check that the 4 bytes were empty but was not
testing what it should as an empty string is `0` bytes long.

The whole must be verified.

Use `memcmp` where it is obvious it is not doing a string comparison.

Casting to `const char *` is not necessary as input, the type are
already the right ones.

It could not be before as `result` was with the wrong type.

Results type should only be an array of char, not an array of pointers.

Adapt tox file from `compile_and_test_for_board.py`.

`tox` is still not working without errors but gives way to start
refactoring.

This script provides functionality to easily backport a merged pull request to
a release branch.

It relies of having a `github` API token stored in `~/.riotgithubtoken` by
default.

The script works by fetching information from the supplied **merged** pull
request. It then looks for the last release branch.
A temporary git `worktree` with a new branch is created based on this release
branch. All commits from the pull request are then cherry-picked into this
branch which is then pushed to `origin`.
It then creates a new pull request on `github` with a reference to the original
pull request. It optionally puts a comment under the original pull request to
the new backport pull request.

Co-authored-by: Gaëtan Harter <gaetan.harter@fu-berlin.de>

sys/shell: ensure character is flushed when echoing.

Currently the constructed NA for a delayed NA case is neither used nor
released nor does it get an IPv6 header to be used properly. This fixes
that case.

 gnrc_ipv6_nib: fix iteration conditions for cache-out

gnrc_tcp: syn_rcvd pkt loss fix

Documentation: fix dead links

pyterm: use python3 by default

When working on the previous commit I was unsure if a
garbage-collectible entry should remain in the list, so I added this
comment so I don't have to wonder about this in the future ;-).

The link to nodemcu-devkit-v1.0 was missing 'h' in 'http'.

Other links were missing 'http://' or 'https://' and were pointing
to non-existing components on RIOT's web site.

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>

gnrc_ipv6_nib: release packet when NC entry can't be added

net/sixlowpan: Fixed calculation of fragment size

Fragment size calculation previously failed for devices that are able to
transmit bigger layer 2 PDUs that 802.15.4 devices. This commit fixes the issue.

gnrc_ipv6_nib/nc: remove from _next_removable on remove

Python3 has been the default in our scripts for some time now, but pyterm still
requested python which uses python2 on ubuntu stable.

This pushes toward only needing to install `python3` python
dependencies.

periph/uart: improve documentation

gnrc_netif_ieee802154: drop duplicate broadcast packets (optionally)

Change description to reflect the configurability of the serial
interface.

Also, fix the uart_mode parameter description as the UART will be
configured and not initialized.

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>

atmega: refactor cpu/board code and build/flash variables

To make the CI happy ;-).

When the neighbor cache is full, the packet trying to resolve a
neighbor is not released.

This change fixes that.

sys/ps: Fixed stringification

The `_next_removable` list manages the cache-out of the neighbor cache.
However, when a neighbor cache entry is removed, it is not removed
from that list, which may lead to a segmentation fault when that list is
accessed, since the whole entry (including its list pointer) is zeroed
after removal.

With this change the entry is removed from that list accordingly before
the zeroing happens.

makefiles/toolchain: fix command -v multiple commands

drivers/bmx280: fix dead links

URLs have been changed to:

https://ae-bst.resource.bosch.com/media/_tech/media/datasheets/BST-BMP280-DS001.pdf
https://ae-bst.resource.bosch.com/media/_tech/media/datasheets/BST-BME280-DS002.pdf

)

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>