When using NodePort to connect to an endpoint using UDP, if the endpoint is deleted on
restoration of the endpoint traffic does not flow. This happens because conntrack holds
the state of the connection and the proxy does not correctly clear the conntrack entry
for the stale endpoint.

Introduced a new function to conntrack ClearEntriesForPortNAT that uses the endpointIP
and NodePort to remove the stale conntrack entry and allow traffic to resume when
the endpoint is restored.
Signed-off-by: Jacob Tanenbaum <jtanenba@redhat.com>