The value of tmnxRadProxSrvCacheKeyVendorId specifies
the RADIUS Vendor-Id.
If the value of tmnxRadProxSrvCacheKeyVendorId is equal to zero, the
attribute type specified by tmnxRadProxSrvCacheKeyAttrType must be
used if it appears outside of a Vendor-Specific attribute.
If the value of tmnxRadProxSrvCacheKeyVendorId is not equal to zero, the
attribute type specified by tmnxRadProxSrvCacheKeyAttrType must be
used if it appears as a sub-attribute within a Vendor-Specific attribute
with Vendor-Id equal to the value of tmnxRadProxSrvCacheKeyVendorId.