missing include for `htons`

[raenye]

$ cmake --build build
[...]
[ 71%] Building CXX object examples/basic_client/CMakeFiles/basic_client.dir/main.cpp.o
/home/user/git/sendspin-cpp/examples/basic_client/main.cpp: In member function ‘bool MdnsAdvertiser::start(const string&, uint16_t, const string&)’:
/home/user/git/sendspin-cpp/examples/basic_client/main.cpp:90:13: error: ‘htons’ was not declared in this scope
   90 |             htons(port),          // port (network byte order)
      |             ^~~~~
gmake[2]: *** [examples/basic_client/CMakeFiles/basic_client.dir/build.make:76: examples/basic_client/CMakeFiles/basic_client.dir/main.cpp.o] Error 1
gmake[1]: *** [CMakeFiles/Makefile2:415: examples/basic_client/CMakeFiles/basic_client.dir/all] Error 2
gmake: *** [Makefile:156: all] Error 2

Fixed by adding #include <netinet/in.h> to examples/basic_client/main.cpp.
Target: Linux x86_64.