The value of tmnxPtpPeerUnicastDirection specifies the direction
of packet flow for tmnxPtpPeerUnicastPktType packets (announce,
sync, or delay response). Ordinary slave clocks will only have
entries in tmnxPtpPeerUnicastTable with a tmnxPtpPeerUnicastDirection
of 'rx (1)'. Ordinary master clocks will only have entries with a
tmnxPtpPeerUnicastDirection of 'tx (2)'. Boundary clocks may have
entries in both directions.