ospfd: Fast OSPF convergence

ospfd: Fast OSPF convergence

When considering small networks that have extreme requirements on
availability and thus convergence delay, the timers given in the OSPF RFC
seem a little “conservative”, i.e., the delay between accepted LSAs and the
rate at which LSAs are sent.  Cisco introduced two commands 'timers throttle
lsa all’ and 'timers lsa arrival’, which allow operators to tune these
parameters.

I have been writing a patch to also support 'timers lsa arrival’ fully and
‘timers throttle lsa all’ (without the throttling part) also in quagga.