[openthread] always enable SLAAC in ot-br-posix (#626)
[openthread] always enable SLAAC in ot-br-posix (#626)


openthread/ot-br-posix,openthread/borderrouter,openthread/ot-br-posix,bukepo/borderrouter,bukepo/borderrouter,openthread/ot-br-posix,openthread/ot-br-posix,bukepo/borderrouter,bukepo/borderrouter,openthread/borderrouter,openthread/borderrouter,openthread/ot-br-posix,openthread/borderrouter,openthread/ot-br-posix,openthread/borderrouter,bukepo/borderrouter,openthread/borderrouter