MFC r305860, r306371

r305860:
Add an option called "random" that combined with "ether" can generate a
random MAC address for an Ethernet interface.

PR: 211984
Submitted by: pi@
Reviewed by: gnn, cem, jhb, lidl, rpokala, wblock
Approved by: wblock (manpages)

r306371:
Indicate that this is a locally administered MAC address.

Submitted by: lidl
Differential Revision: https://reviews.freebsd.org/D7903

PR: 226459
Requested by: tobik