network api : reload : don't allow openswitch at all

network api : reload : don't allow openswitch at all

ifupdown2 reload can't work with openswitch until we implement
ovs.

I don't think that too much users are mixing ovs && bridge anyway.

It's possible to use ifupdown2 with ovs for ifup/down with ifupdown script,
but config need to be changed, and I don't have tested too much.
(maybe add a conflict in ifupdown2 package with openvswitch package for now)

Signed-off-by: Alexandre Derumier <aderumier@odiso.com>