Never use events for blocking sockets under Unix.

Events are not needed for this kind of sockets, using wxSOCKET_BLOCK is
supposed to ensure that calling socket IO operations blocks until the bytes
are read/written without dispatching any events.

See #17031.

include/wx/private/socket.h

@@ -308,6 +308,9 @@ public:
 protected:
     wxSocketImpl(wxSocketBase& wxsocket);
 
+    // get the associated socket flags
+    wxSocketFlags GetSocketFlags() const { return m_wxsocket->GetFlags(); }
+
     // true if we're a listening stream socket
     bool m_server;