gui: use basic grid in the network panel

gui: use basic grid in the network panel

Using boxes causes the labels to not align correctly in certain
circumstances. In the following commits we replace the use of boxes with
grids and set the margins and spacing directly on the respective grid.

Signed-off-by: Maximiliano Sandoval <m.sandoval@proxmox.com>
Reviewed-by: Christoph Heiss <c.heiss@proxmox.com>
Tested-by: Christoph Heiss <c.heiss@proxmox.com>
Tested-by: Tested-by: Lukas Wagner <l.wagner@proxmox.com>