The state of this BRI channel. The value inactive means that
the channel does not currently have an active user, either an
ISDN call or an active TDM group. The value active means that
the channel is in use, either by an ISDN call or an active TDM
group. For the D channel, this object will have the value
active if LAPD is using the D channel (either for call control
or X.25), or the value inactive otherwise.