This essentially reverts commit 12d24abba7.
Making the callback _delete_segments_for_network respond to
BEFORE_DELETE network event has created some bugs. In one of them,
it is not possible to delete a routed network, because the segments
cannot be deleted due to the fact that the associated subnets still
exist.
Making _delete_segments_for_network respond to PRECOMMIT_DELETE
introduces a StaleDataError with the standard attributes of the
deleted segments. To work around that, network_db is expired and
read again after notifying the PRECOMMIT_DELETE event in
delete_network in the DB core plug-in.
This also fixes an issue where we could delete the segment ID
of the l3-ha network when deleting a router, leaving all other
routers non-functioning. Moving this to PRECOMMIT_DELETE fixes
it since it is done after we have checked that the network is
not in use and can be deleted.
Closes-Bug: #1697324
Closes-Bug: #1732543
Change-Id: I7c3c4654f183b317647a28d599a538fe460db68f
9dff53ce65
