rstp: Add 'rstp-admin-p2p-mac' and 'rstp-admin-port-state' setters.

rstp: Add 'rstp-admin-p2p-mac' and 'rstp-admin-port-state' setters.

'rstp-admin-port-state' is the Administrative Bridge Port state
variable defined in the 802.1D-2004 standard.  It can be set to
include or exclude a port from the active topology by management
(section 7.4).

operPointToPointMAC and 'rstp-admin-p2p-mac' are a pair of parameters
that permit inspection of, and control over, the administrative and
operational state of the point-to-point status of the MAC entity by
the MAC Relay Entity.  adminPointToPointMAC can be set by management
and its value is reflected on operPointToPointMAC.

Signed-off-by: Daniele Venturino <daniele.venturino@m3s.it>
Acked-by: Jarno Rajahalme <jrajahalme@nicira.com>