Bug 24518

I use two different ISPs for PPP dialup connections. In either ISP,
ppp fails to negitiate DNS server address with following IPCP log
(date, pid and tun device name trimmed):

IPCP: FSM: Using "deflink" as a transport 
IPCP: deflink: State change Initial --> Closed 
IPCP: deflink: LayerStart. 
IPCP: deflink: SendConfigReq(1) state = Closed 
IPCP:  IPADDR[6]  0.0.0.0 
IPCP:  COMPPROTO[6]  16 VJ slots with slot compression 
IPCP:  PRIDNS[6]  0.0.0.0 
IPCP:  SECDNS[6]  0.0.0.0 
IPCP: deflink: State change Closed --> Req-Sent 
IPCP: deflink: RecvConfigReq(151) state = Req-Sent 
IPCP:  IPADDR[6]  210.158.230.5 
IPCP: deflink: SendConfigAck(151) state = Req-Sent 
IPCP:  IPADDR[6]  210.158.230.5 
IPCP: deflink: State change Req-Sent --> Ack-Sent 
IPCP: deflink: RecvConfigRej(1) state = Ack-Sent 
IPCP:  COMPPROTO[6]  16 VJ slots with slot compression 
IPCP:  SECDNS[6]  0.0.0.0 
IPCP: deflink: SendConfigReq(2) state = Ack-Sent 
IPCP:  IPADDR[6]  0.0.0.0 
IPCP: deflink: RecvConfigNak(2) state = Ack-Sent 
IPCP:  IPADDR[6]  210.158.231.184 
IPCP:  IPADDR[6]  changing address: 0.0.0.0  --> 210.158.231.184 
IPCP: deflink: SendConfigReq(3) state = Ack-Sent 
IPCP:  IPADDR[6]  210.158.231.184 
IPCP: deflink: RecvConfigAck(3) state = Ack-Sent 
IPCP: deflink: State change Ack-Sent --> Opened 
IPCP: deflink: LayerUp. 
IPCP: myaddr 210.158.231.184 hisaddr = 210.158.230.5 

i.e. Though only secondary DNS has been rejected, ppp gives up
negotiating primary DNS too.

Fix: By applying following patch, ppp tries to negotiate primary
DNS server if secondary conf-request rejected, or negotiate
secondary if primary rejected:
How-To-Repeat: (described above)