title: source-specific multicast using boost
body: <p>How can I join source-specific multicast (ssm) group using boost? </p>
  
  <p>I'v successfully joined any-source multicast group using </p>
  
  <p><code>set_option( ip::multicast::join_group( mcAddr.to_v4(), ifAddr.to_v4( )));</code></p>
  
  <p>but I have no idea how to set ssm (<code>IP_ADD_SOURCE_MEMBERSHIP</code>). </p>
  
  <p>How can I do it? Thank you.</p>