If proxy.SetAPIServerPort was called multiple times, all calls after the
first one would cause the apiserver address to be set to the default
server address, bypassing the local load-balancer. This was most likely
to occur on RKE2, where the supervisor may be up for a period of time
before it is ready to manage node password secrets, causing the agent
to retry.
Signed-off-by: Brad Davidson <brad.davidson@rancher.com>