The value of tmnxBsxTransPrefEntrySubAddrType specifies
the address type of the subscriber address prefix associated
with this transit prefix policy entry.
tmnxBsxTransPrefEntrySubAddrType can be 'unknown(0)' indicating
the subscriber address prefix is not used for matching. If the
value is not 'unknown(0)' and tmnxBsxTransPrefEntryNetAddrType
is not 'unknown(0)', then tmnxBsxTransPrefEntrySubAddrType must
have the same value as tmnxBsxTransPrefEntryNetAddrType.