Merge pull request #416 from VeijoPesonen/network_status_callback

Mbed OS 5.8 brings support for network interface status change callback

Author: Amanda Butler

docs/reference/api/connectivity/networksocket/EthInterface.md

@@ -15,12 +15,16 @@ To bring up the network interface:
 1. Once you connect the EthInterface, you can use it as a
 target for opening [network sockets](/docs/v5.7/reference/network-socket.html).
 
-### EthInterface example
+### EthInterface examples
 
 Here is an example of an HTTP client program. The program brings up Ethernet as the underlying network interface and uses it to perform an HTTP transaction over a TCPSocket:
 
 [![View code](https://www.mbed.com/embed/?url=https://os.mbed.com/teams/mbed_example/code/TCPSocket_Example/)](https://os.mbed.com/teams/mbed_example/code/TCPSocket_Example/file/6b383744246e/main.cpp)
 
+Here is an example showing how to register a status callback that gets triggered when connection state changes. This also works with other network interfaces if support is provided.
+
+[![View code](https://www.mbed.com/embed/?url=https://os.mbed.com/teams/mbed_example/code/TCPSocket_ConnStateCb_Example/)](https://os.mbed.com/teams/mbed_example/code/TCPSocket_ConnStateCb_Example/file/987d54985478/main.cpp/)
+
 ### Related content
 
 - [Network socket](/docs/v5.7/reference/network-socket.html) API reference overview.