Make mac addr checks disabled by default and add parameter to turn on

[akarasulu]

Right now the default is to check for mac addresses on the network after creating a random mac address to be absolutely certain that no other machine has the same mac address on the network.

This is not always needed. I do not think this should be enabled for the simple default case. There should be a parameter to turn this feature on like MAC_CHECK which can be either true or false. The default should be false.