ospfd: add support for "no router-info [<area|as>] command"

ospfd: add support for "no router-info [<area|as>] command"

frr-reload.py will walk through all config contexts and prepend no to the CLI
command. This requires that the vtysh shell code accepts a full command.

To Reproduce

vtysh -c "conf t" -c "router ospf" -c "router-info area"
vtysh -c "conf t" -c "router ospf" -c "no router-info area"
% Unknown command: no router-info area
vtysh -c "conf t" -c "router ospf" -c "no router-info"

Signed-off-by: Christian Breunig <christian@breunig.cc>