Change MAC address input format

Set the base of strtol to 16 when parsing MAC address. This means the address can be specified in the much more human-friendly format

M540 PBE:EF:12:34:56:78

The variant with "0x" preceding each byte still works just as earlier, this small change just makes the 0x optional.
Remember second strtol as well

Same change to the strtol a few lines down, affecting the last byte of the MAC address.
Merge pull request #7 from jstck/patch-1

Change MAC address input format