MFC r318160, 318176: Persistently store NIC's hardware MAC address, and add

MFC r318160, 318176: Persistently store NIC's hardware MAC address, and add
a way to retrive it

NOTE: Due to restructuring, the merges didn't apply cleanly; the resulting
change is almost identical to what went into stable/11, but in some cases in
different locations.

The MAC address reported by `ifconfig ${nic} ether' does not always match
the address in the hardware, as reported by the driver during attach. In
particular, NICs which are components of a lagg(4) interface all report the
same MAC.

When attaching, the NIC driver passes the MAC address it read from the
hardware as an argument to ether_ifattach(). Keep a second copy of it, and
create ioctl(SIOCGHWADDR) to return it. Teach `ifconfig' to report it along
with the active MAC address.

PR:		194386

git-svn-id: svn://svn.freebsd.org/base/stable/10@318430 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f