Add the ability to change the vlan operation mode.

This adds a vlan capability field to etherswitch_info structure and some
definitions of ports flags.

It adds the support to global config parameters which right now is used
only to switch between the vlan modes, but it is intended to be extended
to support the setup of others parameters (STP, mirror, etc.).

Submitted by:	Luiz Otavio O Souza <loos.br@gmail.com>
Reviewed by:	ray
Add vlan configuration support to etherswitchcfg.

This adds the support to the config keyword (vlan operation mode), ports
flags, prints the vlan mode and vlan capabilities. It also adds some basic
information to usage() and support the keyword 'help' as a shortcut to
usage(). The manual page is also updated with the new options.

Submitted by:	Luiz Otavio O Souza <loos.br@gmail.com>
Reviewed by:	ray
Correctly mark the CPU port.

Submitted by:	Luiz Otavio O Souza <loos.br@gmail.com>
Reviewed by:	ray
Fix the ukswitch code to work with the new vlan changes:

* Fix API changes;
* remove unused code;
* Allow some switches to be used that don't expose a set of PHY
  registers for the CPU facing port (eg the ADM6996 for the Ubiquiti
  Routerstation.)

Submitted by:	Luiz Otavio O Souza <loos.br@gmail.com>
Reviewed by:	ray
Modify the routerstation config to use ukswitch for now.

Until an ADM6996 driver shows up, this allows for the two switch
ports to be used.

Submitted by:	Luiz Otavio O Souza <loos.br@gmail.com>
Reviewed by:	ray
Bring in a basic ethernet switch driver for the IP17x series of
switches.

These are notably found on some AR71xx based Mikrotik boards.

Submitted by:	Luiz Otavio O Souza <loos.br@gmail.com>
Reviewed by:	ray
mdoc: new sentence, new line.
Remove EOL whitespace.
Revert r250339 as apparently it is more clutter than help.

Sponsored by:	EMC / Isilon storage division
Requested by:	jhb
Minor improvements.