Fix possible compile error using former GLib2 version
    
    We require GLib 2.50 but G_SOURCE_FUNC was introduced in version
    2.58. Do the conversion instead of using G_SOURCE_FUNC macro.
    
    Signed-off-by: Frediano Ziglio <freddy77@gmail.com>
    Acked-by: Victor Toso <victortoso@redhat.com>
    (cherry picked from commit d0b5f80adaef757ebfa81d1ab1c6561697243dc9)
    
    patch_name: 0004-Fix-possible-compile-error-using-former-GLib2-versio.patch
    present_in_specfile: true
    location_in_specfile: 4
    squash_commits: true