doc: net: Add networking changes to 2.1 release note

Initial set of networking changes in 2.1 release.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>

doc/releases/release-notes-2.1.rst

@@ -36,7 +36,53 @@ Drivers and Sensors
 Networking
 **********
 
-* TBD
+* Added new TCP stack implementation. The new TCP stack is still experimental
+  and is turned off by default. Users wanting to experiment with it can set
+  :option:`CONFIG_NET_TCP2` Kconfig option.
+* Added support for running MQTT protocol on top of a Websocket connection.
+* Added infrastructure for testing network samples in automatic way.
+* Added support for enabling DNS in LWM2M.
+* Added support for resetting network statistics in net-shell.
+* Added support for getting statistics about the time it took to receive or send
+  a network packet.
+* Added support for sending a PPP Echo-Reply packet when a Echo-Request packet
+  is received.
+* Added CC13xx / CC26xx device drivers for IEEE 802.15.4.
+* Added TCP/UDP socket offload with TLS for eswifi network driver.
+* Added support for sending multiple SNTP requests to increase reliability.
+* Added support for choosing a default network protocol in socket() call.
+* Added support for selecting either native IP stack, which is the default, or
+  offloaded IP stack. This can save ROM and RAM as we do not need to enable
+  network functionality that is not going to be used in the network device.
+* Added support for LWM2M client initiated de-register.
+* Updated the supported version of OpenThread.
+* Updated OpenThread configuration to use mbedTLS provided by Zephyr.
+* Various fixes to TCP connection establishment.
+* Fixed delivery of multicast packets to all listening sockets.
+* Fixed network interface initialization when using socket offloading.
+* Fixed initial message id seed value for sent CoAP messages.
+* Fixed selection of network interface when using "net ping" command to send
+  ICMPv4 echo-request packet.
+* Networking sample changes for:
+
+  .. rst-class:: rst-columns
+
+     - http_client
+     - dumb_http_server_mt
+     - dumb_http_server
+     - echo_server
+     - mqtt_publisher
+     - zperf
+
+* Network device driver changes for:
+
+  .. rst-class:: rst-columns
+
+     - Ethernet enc424j600 (new driver)
+     - Ethernet enc28j60
+     - Ethernet stm32
+     - WiFi simplelink
+     - Ethernet DesignWare (removed)
 
 Bluetooth
 *********