When we fail to aquire a lease, our lease expires without a sucessful

renewal, or we lose link, be more forceful about clearing interface
state so another interface that connects to the same network has a
chance of working.  This doesn't address attemping to connect to both at
once, but appears to allow unplugging from a wired interface and then
inserting a wireless card that associates with an AP bridged to the same
LAN.

sbin/dhclient/dhclient-script

@@ -247,6 +247,7 @@ EXPIRE|FAIL)
 		delete_old_address
 		delete_old_routes
 	fi
+	ifconfig $interface delete
 	# XXX Why add alias we just deleted above?
 	add_new_alias
 	if [ -f /etc/resolv.conf.save ]; then