t_unbind - disable a transport endpoint
t_unbind() disables the transport endpoint specified by fd which was
previously bound by t_bind(3N). On completion of this call, no further
data or events destined for this transport endpoint will be accepted by
the transport provider.
0 on success.
-1 on failure and sets t_errno to indicate the error.
TBADF The specified file descriptor does not refer to a
TLOOK An asynchronous event has occurred on this trans-
TOUTSTATE The function was issued in the wrong sequence.
TSYSERR The function failed due to a system error and set
errno to indicate the error.
21 January 1990 T_UNBIND(3N)