Once the packet buffer is full on heavy network load, gnrc_netif_hdr_build may return NULL. In that case, the following unchecked access to hdr->data leads to a crash.

boards/hifive1: fix CLOCK_CORECLOCK

gnrc_icmpv6: release in error cases of demux

boards/sensebox_samd21: Add MTD definition

esp8266: esp_wifi netdev driver

net/nanocoap: verify simple reply buffer

net/netreg: fix static netreg init macros

boards/arduino*: Added/refactored params for W5100

sys/base64: Add size estimation functions

gnrc_ipv6_nib: activate SLAAC on border router

When the size of a received frame is checked, always the total length should be used instead of the length of the first lwIP pbuf in the pbuf chain. Otherwise, the check that the length does not exceed ETHERNET_MAX_LEN will always be true since the maximum size of one lwIP pbuf in a pbuf chain is 512 bytes.

Receiption of a frame in _esp_wifi_recv_cb while sending has no effect and should be possible to increases the performance.

net/nanocoap: validate option length

Although only the station interface is needed, the WiFi interface has to be used in SoftAP + Station mode. Otherwise the send function blocks sporadically. Since the SoftAP interface is not used, it is configured with a hidden SSID and a long beacon interval. Connections from other stations are not allowed.

A timeout was introduced if sending a frame takes to long time. In that case the WiFi interface disconnects and reconnects automatically to recover.

A reconnect timer is used to try to reconnect every 20 secons if WiFi interface is in disconnected or connecting state.

Due to performance reasons _esp_wifi_recv_cb and _send have to be executed in IRAM.

To avoid conflicts on receiption of a frame while sending, _esp_wifi_recv_cb should not executed while a frame is in transmission

Overriding ethernet_input function _esp_wifi_recv_cb is only used when the WiFi interface is in connected state.

wifi_station_connect and wifi_stattion_disconnect never produce errors. Thus, error handling can be removed.

Different connection states defined to be able to realize a better connect/reconnect handling

Some SDK interrupt service routines obviously use malloc/free in the interrupt context. Because the rmutex-based lock/unlock approach of the malloc/free function suite of the newlib does not work in the interrupt context, the SDK memory management functions MUST therefore be used. To use the same memory management functions in RIOT as in the SDK, the malloc/free function suite has to be replaced by wrapper functions.

Since complete MAC frames are handled, ETHERNET_MAX_LEN has to be used instead of ETHERNET_DATA_LEN for receive buffer size and length check.

Fixes sporadic blocking of the wifi thread in esp_wifi_recv_cb function under heavy network load conditions when frames are coming in faster than they can be processed. Since esp_wifi_recv_cb function is not executed in interrupt context, the msg_send function used for ISR event can block when the message queue is full. With this change esp_wifi can be flooded with icmpv6 packets of maximum size without any problems over hours.