debian: Fix OVS upgrade dependencies.

debian: Fix OVS upgrade dependencies.

Commit 0dcc739e7a28 ("debian: Move ovs-lib to openvswitch-common.")
shifted a file between debian packages, but didn't update the
destination package annotations to indicate that it replaces a file
from earlier versions of the source package.

As a result, if one installs openvswitch-switch-2.5* (or earlier) and
then tries to upgrade to openvswitch-{switch,common}-2.5.90+, the
install of openvswitch-common will fail like the following:

dpkg: error processing archive
/tmp/openvswitch-common_2.5.90-1_amd64.deb (--install):
trying to overwrite '/usr/share/openvswitch/scripts/ovs-lib', which is
also in package openvswitch-switch 2.5.0-1

Fix the issue by adding "Replaces" and "Breaks" tags to the new
openvswitch-common section of debian/control.

Fixes: 0dcc739e7a28 ("debian: Move ovs-lib to openvswitch-common.")
Signed-off-by: Joe Stringer <joe@ovn.org>
Acked-by: Daniele Di Proietto <diproiettod@vmware.com>