Extend and rename wxSocketImpl::UnblockAndRegisterWithEventLoop()

In addition to unblocking and registering the socket, also support using
this function to make the socket blocking and unregistering it from the
event loop, if its flags include wxSOCKET_BLOCK.

This was already half-done by wxMSW, which took wxSOCKET_BLOCK presence
into account in its implementation, but not by the Unix implementation.
Now do it under all platforms, as this will be useful for switching a
previously non-blocking socket to blocking mode.

Finally, rename the function to better reflect what it really does.

See #12886.

include/wx/unix/private/sockunix.h

@@ -73,12 +73,13 @@ private:
         wxCloseSocket(m_fd);
     }
 
-    virtual void UnblockAndRegisterWithEventLoop() wxOVERRIDE
+    virtual void UpdateBlockingState() wxOVERRIDE
     {
-        int trueArg = 1;
-        ioctl(m_fd, FIONBIO, &trueArg);
+        // Make this int and not bool to allow passing it to ioctl().
+        const int isBlocking = (GetSocketFlags() & wxSOCKET_BLOCK) != 0;
+        ioctl(m_fd, FIONBIO, &isBlocking);
 
-        EnableEvents();
+        DoEnableEvents(wxSOCKET_INPUT_FLAG | wxSOCKET_OUTPUT_FLAG, !isBlocking);
     }
 
     // enable or disable notifications for socket input/output events