Ethernet: Print the Length/Type field as length when needed

Ethernet: Print the Length/Type field as length when needed

Reference: IEEE Std 802.3-2012
"If the value of this field is less than or equal to 1500 decimal
(05DC hexadecimal), then the Length/Type field indicates the number
of MAC client data octets contained in the subsequent MAC Client Data
field of the basic frame (Length interpretation)."

Update the output of a test accordingly.