Given the ifIndex of an internal ATM interface, and
VPI/VCI, provides the ifIndex of a Frame Relay
interface and DLCI, if such mapping exists.
The value of ifType for an internal ATM interface is
propVirtual(53). For every such interface on the
switch, this table contains an entry for each virtual
channel link (VCL) that maps to a frame relay
connection. Entries in this table come and go as the
corresponding frame relay connections come and go.