Indicates the amount of time in milliseconds for our T4 timer.
The T4 timer is a debounce timer which is used to shield the
upper layers from short glitches at the S/T interface. Spurious
problems of short duration will not be reported to the upper
layers until the T4 timer expires. The T4 timer is started when
leaving state F7 or F8 upon the reception of INFO 0. The corresponding
Deactivation Indication will be delivered to layer 2 only if layer 1
does not enter an active state before expiration of this timer. (Note
that a value of 0 indicates the timer is disabled).