Dormant static default route over unnumbered PPP interface

[Kenth Eriksson]

Static default route over unnumbered PPP interface is stuck in dormant state. Manually installing this route in kernel with 'ip route' does not give any issues. 

bird> show static
0.0.0.0/0
	via 10.210.137.96 (dormant)

bird> show route
Table master4:
10.210.137.97/32     unicast [direct1 10:55:13.947] * (255)
	dev lo
10.210.137.96/32     unicast [direct1 10:55:19.252] * (255)
	dev p1-1-1-1-2
10.0.0.0/20          unicast [direct1 10:54:37.104] * (255)
	dev eth0

# ifconfig p1-1-1-1-2
p1-1-1-1-2 Link encap:Point-to-Point Protocol  
          inet addr:10.210.137.97  P-t-P:10.210.137.96  Mask:255.255.255.255
          UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1492  Metric:1
          RX packets:1178 errors:0 dropped:2 overruns:0 frame:0
          TX packets:782 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:3 
          RX bytes:62113 (60.6 KiB)  TX bytes:57060 (55.7 KiB)