ospfd: handling of OSPF_AREA_RANGE_ADVERTISE flag

ospfd: handling of OSPF_AREA_RANGE_ADVERTISE flag

Issue: # https://github.com/FRRouting/frr/issues/1836

Issue 1: if the router ospf current configuration is "area 0.0.0.2
range 1.0.0.0/24 cost 23" and user try to configure "area 0.0.0.2
range 1.0.0.0/24 not-advertise", the existing o/p is "area 0.0.0.2
range 1.0.0.0/24 cost 23 not-advertise". The keywords "not-advertise"
& "cost" are multually exclusive, so they should not come together.
The vice versa way configuration is working fine.

Fix: When ospf area range "not-advertise", the cost should be initialized
to OSPF_AREA_RANGE_COST_UNSPEC.

Issue 2: if the router ospf current configuration "area 0.0.0.2 range
1.0.0.0/24 substitute 2.0.0.0/24" and user try to configure "area 0.0.0.2
range 1.0.0.0/24 not-advertise" the existing o/p is "area 0.0.0.2 range
1.0.0.0/24 not-advertise substitute 2.0.0.0/24". The keywords
"not-advertise" & "substiture" are multually exclusive, so they should
not come together. The vice versa way configuration is working fine.

Fix: When ospf area range "not-advertise" is configured,
ospf_area_range_substitute_unset() should be get called.

Issue 3: if the router ospf6 current configuration is "area 0.0.0.2
range 2001::/64 cost 23" and user try to configure "area 0.0.0.2 range
2001::/64 advertise", the existing o/p is area 0.0.0.2 range 2001::/64.
The keyword "cost 23" disappears.

Fix: When ospf area range "advertise" is configured and the range is not
NULL, the cost should not be modified.

Signed-off-by: Sarita Patra <saritap@vmware.com>