OSPF: Allow ifaces with host address as unnumbered PtP or PtMP ifaces

Ifaces with host address (/32) were forced to be stubby, but now they
can be used as PtP or PtMP. For these ifaces we need to:

 - Do not force stub mode
 - Accept packets from any IP as local
 - Accept any configured neighbor as local
 - Detect ifaces properly as unnumbered
 - Use ONLINK flag for nexthops