applet: do not skip wifi slave connections

If slave connection is a wifi connection we should still display it
Otherwise this AP gets scanned regardless, but when user clicks it new
network is created in NM's configuation - which is unlikely what user desired

Signed-off-by: Nikolay Martynov <mar.kolya@gmail.com>

https://mail.gnome.org/archives/networkmanager-list/2017-May/msg00041.html
https://github.com/NetworkManager/network-manager-applet/pull/1