Only use BIA option when setting fully random MAC

macchanger 1.6.0 added -b / --bia option to control whether locally
administered bit should be set on the randomly generated MACs. If this option
is specified, locally administered bit is cleared, and it's set otherwise.

This option is considered when generating fully random MAC (-r / --random), but
also when setting random vendor MACs (-e / --endding, -a / --another, -A). As
locally administered bit is part of the first MAC octet, which is part of OUI,
clearing the bit (default behaviour when -b is not used) breaks all these
random vendor MAC modes, setting MACs that are not for any recognized vendor.

This fixes makes macchanger set or unset locally administered bit when
generating fully random MAC.  Use of --bia option in combination with other
option than --random generates warning.

Upstream bug report:
https://github.com/alobbs/macchanger/issues/1