[security-policy] remove assertfrom Get/SetSecurityPolicy() (#6464)
[security-policy] remove assertfrom Get/SetSecurityPolicy() (#6464)


srickardti/openthread,openthread/openthread,abtink/openthread,jwhui/openthread,openthread/openthread,jwhui/openthread,jwhui/openthread,jwhui/openthread,abtink/openthread,srickardti/openthread,openthread/openthread,openthread/openthread,abtink/openthread,srickardti/openthread,srickardti/openthread,abtink/openthread