Accton 1.6.1

Hi 
I just created a branch from 1.6.1 for a few Accton devices.  These are for immediate requests for ONIE certification based on existing code.  The first submit is for AS4600-54X.
Allowing the HW vendor to tack on their version string is a good idea.  This could be done a little more generically though.  Something like VENDOR_ONIE_VERSION, if set can be appended as needed.