ofproto-dpif: Don't poll ports when nothing changes

ofproto-dpif: Don't poll ports when nothing changes

Previously, as part of ofproto-dpif run() processing, we would loop
through all ports and poll for changes to carrier, bfd, cfm and lacp
status. This information is used to determine whether bundles may be
enabled, and to perform revalidation when needed.

This patch makes the bfd, cfm, lacp and stp modules aware of the new
global connectivity_seq, notifying on changes in port status. We can
then use connectivity_seq to check if anything has changed before
looping through all ports in ofproto-dpif. In a test environment of 5000
internal ports and 50 tunnel ports with bfd, this reduces average CPU
usage of the main thread from about 35% to about 25%.

Signed-off-by: Joe Stringer <joestringer@nicira.com>
Signed-off-by: Ethan Jackson <ethan@nicira.com>
Acked-by: Ethan Jackson <ethan@nicira.com>