[posix-trel] retry adding interface address if failed (#7047)
[posix-trel] retry adding interface address if failed (#7047)

This commit enhances TREL UDP6 to retry adding the link-local
interface address until it's successful.
abtink/openthread,openthread/openthread,jwhui/openthread,srickardti/openthread,srickardti/openthread,abtink/openthread,jwhui/openthread,srickardti/openthread,abtink/openthread,openthread/openthread,openthread/openthread,openthread/openthread,srickardti/openthread,abtink/openthread,jwhui/openthread,jwhui/openthread