Notify about port create/update unconditionally

Notify about port create/update unconditionally

The notification about port create/update should be done no matter
if host (or any other field) was changed or not - it should be up to
handler to decide how to handle it.

This also fixes the bug when there was actually no notification to l3
dvr agent on compute node on new port creation:
_get_host_port_if_changed() always returned None - this is a regression
from commit 2ee08c3464c53abaf9bc5493132ad7958611e3b8

Closes-Bug: #1521524
Change-Id: I5bb416d2aaab632526f06a5620c0a4ea96340d21