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

This change fixes that.

drivers: add support for SHT2x (I2C temp and humidity sensor)

cpu/stm32_common: fix UART documentation

gnrc: nib: fix DOXYGE -> DOXYGEN typo

Don't include overridden typedefs into doxygen as otherwise,
they'll appear twice.

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

Several parts were inspired by a driver written by:
  George Psimenos (gp7g14@soton.ac.uk)
  Steffen Robertz (steffen.robertz@rwth-aachen.de)

cpu/esp32: GPIO macro cleanup in periph_cpu.h

gnrc_sixlowpan_iphc: fix _compressible()

tests/gnrc_tcp_*: remove default PORT for native

shell_commands: adapt ping6 to original-ping-like implementation

drivers/w5100: Fixed netdev_driver_t::recv() API

When either `gnrc_sixlowpan_iphc_nhc` or `gnrc_udp` is not compiled
in `_compressible()` never returns `true`. This causes the
`dispatch` snip in `gnrc_sixlowpan_iphc_send()` to be of length 0,
meaning `dispatch->data` is `NULL`, causing possible crashes when
trying to send IPv6 packets over 6LoWPAN without NHC or UDP.

cpu/fe310: Add call to periph_init()

sam0_common: check ADC_NUMOF on adc_init()

cpu/sam0_common: update README for SAML1x addition

The default macros GPIO_PIN and GPIO_UNDEF do not have to be overridden. The GPIO_PIN macro definition was even wrong for 40 GPIOs without splitting into ports, even if that did not lead to erroneous behavior.

Fix hdc1000 renew interval documentation

chacha20poly1305: Initial implementation of AEAD cipher.

Loosely based on [the original ping] and [netutil]'s ping

New features (compared to old RIOT version):
 - non-positional parameters
 - Better duplicate detection (addresses #9387)
 - Better asynchronous behavior
 - Potential for future move to `sock_ip`
 - (Optional) DNS-support
 - Multithreading-safe (in case shell-command handler gets called
   from multiple threads)

[the original ping]: http://ftp.arl.army.mil/~mike/ping.html
[netutil]: https://www.gnu.org/software/inetutils/

The documentation refers to the `HDC1000_PARAM_RENEW_INTERVAL` as
`HDC1000_RENEW_INTERVAL`.

drivers/cc110x: Fixed MTU calculation

Add a test case to the crypto tests testing the chacha20poly1305
algorithm with the test vectors from rfc 8439.

shell/ifconfig: Add L2-PDU info

Rewrite the README to reflect the recent addition of SAMR30 and
SAML10/SAML11.

sam0 flashpage: wait for READY bit in INTFLAG after write command

release-notes.txt: Add Release 2018.10.1 notes

shell/ifconfig: Fixed stringification

When IPv6 is enabled, the MTU is given. So users(*) sending IPv6 packets can
easily figure out what the supported maximum protocol unit is.

However, when IPv6 is disabled and a user wants to send layer 2 frames directly,
no information about the maximum PDU is available using the shell.

When 6LoWPAN is used, a user may be interested in the layer 2 PDU as well in
order to avoid layer 2 fragmentation.

This PR adds the L2-PDU info to the output of the ifconfig shell command, which
is printed regardless of the use of IPv6.

(*): Here "users" refers to human beings interacting with the shell.
Applications can get the maximum PDU of each layer more easily using
gnrc_netapi_get() with NETOPT_MAX_PACKET_SIZE instead of using a shell command.

cpu/native: fix race in thread_yield_higher()

net stats: move layer 2 netstats from netdev driver to gnrc_netif

netdev_driver_t::get(NETOPT_MAX_PACKET_SIZE) used to return the maximum frame
size instead of the maximum layer 2 PDU size.

Introduced CC110X_L2_HDR_SIZE to get rid of magic numbers.