gnrc_sixlowpan_frag: check if own message queue is full

gnrc_sixlowpan_frag: release packet rbuf_add error cases

Otherwise, there will be leaks ;-).

Otherwise, there will be leaks ;-).

When issueing the sending of the next fragment the current version of
`gnrc_sixlowpan_frag` doesn't check if the queue is full. This leads to
leakage of the packet buffer, since when it is full, the package never
gets released.

This change adds a checks and error exits in case the queue is full.

 print_toolchain_versions.sh: add xtensa toolchains

netdev_driver_t::recv(): Clarified documentation

esp_now: avoid parsing IPv6 header in netdev driver

Some drivers return on netdev_driver_t::recv() not the actual frame size, but
an upper bound estimation of it. The upper layer code is already prepared to
handle that. This brings the doc in sync with the code.

Avoids parsing IPv6 packets to determine destination address.
Allows using 6Lo over ESP-NOW, which is required due to the low MTU of
ESP-NOW.

Co-authored-by: Gunar Schorcht <gunar@schorcht.net>

Clarified in the documentation how netdev_driver_t::recv() should behave in case
the size of the buffer in parameter buf (indicated by parameter len) is to small
to fit the received frame.

netdev_driver_t::recv does on of three things:
 - Receive the frame
 - Drop it
 - Get (an estimation of) the size of the frame

The brief section of the documentation was changed to reflect this. (And it
starts with the least obvious thing in the hope readers of the API stumble upon
it...)

Removed the invalid precondition in netdev_driver_t::recv that the buffer never
NULL and the length positive. (In the "get message size" case both is wrong, in
the drop message case the first part is wrong.)

esp_now: fix doxygen groups

tests/posix_semaphore: increase timeout margin

dist/tools: add support for PyOCD programmer/debugger

drivers/at: add function to read raw data bytes from modem

drivers/sx127x: remove irq_disable/irq_restore around spi transfers

gnrc_sixlowpan: amend gnrc_netapi introduction

 gnrc_netif: remove superfluous GNRC_NETIF_FLAGS_MAC_*

boards/nucleo-l496zg: use lpuart1 as stdio interface

net/ble: add generic advertisement data (AD) processing helper

cpu: esp_common added for common modules of ESP SoCs

Co-authored-by: Vincent Dupont <vincent@otakeys.com>

Co-authored-by: Vincent Dupont <vincent@otakeys.com>

 gnrc_ipv6_nib: use correct reverse-translate for ARSM-less NCE

The current implementation uses the assumption that the IPv6 address is
always based on an EUI-64, which it doesn't has to.