mka: Fix an incorrect update of participant->to_use_sak

mka: Fix an incorrect update of participant->to_use_sak

API ieee802_1x_mka_decode_dist_sak_body() wrongly puts
participant->to_use_sak to TRUE, if Distributed SAK Parameter Set of
length 0 is received. In MACsec PSK mode, this stale incorrect value can
create problems while re-establishing CA. In MACsec PSK mode, CA goes
down if interface goes down and ideally we should be able to
re-establish the CA once interface comes up.

Signed-off-by: Badrish Adiga H R <badrish.adigahr@gmail.com>