ipro1000: Upgrade to FreeBSD 13.1.

Includes support for new I219 device families.

Taken from the 13.1 releng branch (currently on "beta 2" status.)
Tested in QEMU and VMware. The "e1000" device works OK in QEMU,
"e1000e" does not anymore, but reportedly the FreeBSD devs say
it does on bare metal, so this is probably a QEMU bug (it doesn't
seem to be a commonly used device.)

drivers/network: Move ethernet drivers to an "ether" subdirectory.

Now that there is also a "tap" driver in here, and the WiFi drivers
are also in a subdirectory, moving the physical ethernet device drivers
to a subdirectory also makes sense.

(Briefly) discussed on the mailing lists.