In addition to showing basic UDP send/receive example, it helps to test
corner-case when dealing with 0-length UDP packets.
Change-Id: I08c0adf1cf9b6a6f1f7090b237d0497c2ec13cdf
Related: OS#2219
We should have doxygen documentation for all libosmo-* APIs.
libosmo-netif is currently devoid of any API docs. Let's start with the
stream and datagram socket related functions.
Change-Id: I589a5e60d9df2b8a65fbaf68f80e3ae0039d8c2a