[gnome-control-center] network: Fix runtime warning

[Bastien Nocera <hadess src gnome org>]

commit 17c6563e694b8f1702bd740b78b0e06c2ff755e2
Author: Bastien Nocera <hadess hadess net>
Date:   Tue Jan 23 10:58:00 2018 +0100

    network: Fix runtime warning
    
    Gtk-WARNING **: Failed to set property GtkImage.icon-size to button: Could not parse integer 'button'
    
    Replaced it with the non-symbolic value "4".

 panels/network/wifi.ui |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)
---
diff --git a/panels/network/wifi.ui b/panels/network/wifi.ui
index cde1456..8c0734f 100644
--- a/panels/network/wifi.ui
+++ b/panels/network/wifi.ui
@@ -215,7 +215,8 @@
                                 <property name="visible">True</property>
                                 <property name="can_focus">False</property>
                                 <property name="icon_name">view-refresh-symbolic</property>
-                                <property name="icon_size">button</property>
+                                <!-- GTK_ICON_SIZE_BUTTON -->
+                                <property name="icon_size">4</property>
                               </object>
                             </child>
                             <style>