ofproto-dpif: Only run bundles when lacp or bonds are enabled

ofproto-dpif: Only run bundles when lacp or bonds are enabled

When dealing with a large number of ports, bundle_run() and
bundle_wait() add significant unnecessary processing to the main run
loop, even when there are no bonds and lacp is not configured. This
patch skips such execution if it is unneeded, reducing average CPU usage
of the main thread from about 25% to about 20% in a test environment of
5000 internal ports and 50 tunnel ports running bfd.

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