o Extend the if_data structure with an ifi_link_state field and
provide the corresponding defines for the valid states.
o The mii_linkchg() callback updates the ifi_link_state field
and calls rt_ifmsg() to notify listeners on the routing socket
in addition to the kqueue KNOTE.
o If vlans are configured on a physical interface notify and update
all vlan pseudo devices as well with the vlan_link_state() callback.
No objections by: sam, wpaul, ru, bms
Brucification by: bde
127d7b2d2d