network: Reference icon-name that exists in wifi panel desktop file

Similarly to fd651824, rpminspect catched that gnome-wifi-panel.desktop references an icon name that doesn't exist.

Desktop file /usr/share/applications/gnome-wifi-panel.desktop on x86_64 references icon network-wireless but no subpackages contain network-wireless

The way the icon lookup works will suffix it with "-symbolic", resulting in "network-wireless-symbolic", which exists.

While MR !2452 (merged) provided settings icons for various panels, it didn't for the Wifi panel.