The type of line monitoring packets being sent and received on
this PPP link. Note that this can be deduced from the values of
tmnxPppKaPeriod and tmnxPppQuality. One can find out whether
lqm or keepalive is enabled or not. That is, lqm is enabled
(keepalive is disabled) if tmnxPppQuality is not zero; and
keepalive is enabled if tmnxPppKaPeriod is not zero and
tmnxPppQuality is zero. If tmnxPppQuality and tmnxPppKaPeriod
are both set to zero, no line monitoring is used.