libteam: add API for carrier control

Signed-off-by: Flavio Leitner <fbl@redhat.com>
lacp: fix carrier state

Fix to bring up or down the master depending on its ports states

Signed-off-by: Flavio Leitner <fbl@redhat.com>
lacp: add min_ports parameter

This parameter works as a threshold for the lacp runner
to decide whether to set the carrier up or down.

Signed-off-by: Flavio Leitner <fbl@redhat.com>