Slightly rephrase note in tenant networking docs
Slightly rephrase note in tenant networking docs

* Taken out of context, the note could cause a bit of confusion,
  explicitly note the difference between flat and neutron networking.

Change-Id: Ief0cf6861b510af50574fdf623526a1560301caf
Signed-off-by: Jan Gutter <877e59bd3bf4b032f5144e1f34e440b243c7f5c4@netronome.com>

openstack/ironic,openstack/ironic