bridge: don't bring up internal ports by default.

It should be an administrator task to bring up devices as they
are configured properly.

Currently, Fedora is deleting the bridges when the interface is
brought down. Therefore, there is no bridge on the next boot and
the initscripts can apply the networking configuration properly
for a new bridge.

However, if the system didn't execute ifdown for some reason, the
bridge is left in the ovsdb and since internal ports are brought
up by default, there is no way for initscripts to known if the
adminitrator has already configured it or not.

This patch reverts commit bef071a5fdf8e2dd87677b04b3cf7a8f5094edcb
(bridge: Always "up" internal devices.).

Signed-off-by: Flavio Leitner <fbl@redhat.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>