Why "wake on LAN" feature fails to remain persisten across reboots on certain"HP t6XX" thinkclient system with "r8169" based NIC in RHEL6?

Issue

• We see that Wake-on-lan feature fails to remain persistently active after reboot though the underlying NIC indicates that it is active on the interface.
• On the system we see following status for the Wake-on-lan option on the NIC:

# ethtool eth0 
Settings for eth0:
    Supported ports: [ TP MII ]
    Supported link modes:   10baseT/Half 10baseT/Full 
                            100baseT/Half 100baseT/Full 
                            1000baseT/Half 1000baseT/Full 
    Supported pause frame use: No
    Supports auto-negotiation: Yes
    Advertised link modes:  10baseT/Half 10baseT/Full 
                            100baseT/Half 100baseT/Full 
                            1000baseT/Full 
    Advertised pause frame use: Symmetric Receive-only
    Advertised auto-negotiation: Yes
    Link partner advertised link modes:  10baseT/Half 10baseT/Full 
                                         100baseT/Half 100baseT/Full 
    Link partner advertised pause frame use: No
    Link partner advertised auto-negotiation: Yes
    Speed: 100Mb/s
    Duplex: Full
    Port: MII
    PHYAD: 0
    Transceiver: internal
    Auto-negotiation: on
    Supports Wake-on: pumbg  <<--
    Wake-on: g <--
    Current message level: 0x00000033 (51)
                   drv probe ifdown ifup
    Link detected: yes

• It only remains persistent after defining ETHTOOL_OPTS="-s eth0 wol g parameter in the interface configuration.