The value of tmnxOamVprnTrL3MapRteDestMask indicates the number
of prefix bits (prefix width) to be &-ed with IP address in
tmnxOamVprnTrL3MapRteDestAddr.
This object was obsoleted in release 4.0 and replaced with
InetAddress object tmnxOamVprnTrL3MapDestMaskLen.