Encode entropy value in UDP source port when requested per RFC 7510. CLI already has "src-port-is-entropy", use zero UDP source port in API to avoid breaking changes, since zero port is not something to be used in wild. Also, mark UDP encapsualtion API as mp-safe as already done for CLI. Type: feature Change-Id: Ieb61ee11e058179ed566ff1f251a3391eb169d52 Signed-off-by: Vladislav Grishenko <themiron@yandex-team.ru>