Remove remnants of classful behavior in route(8).

[melifaro]

Summary

As reported in bin/237391, route(8) treats some addresses as network addresses:

route -nv get 10.0.0.0

RTA_DST: inet 10.0.0.0; RTA_NETMASK: inet 255.0.0.0; RTA_IFP: link ; RTM_GET: Report Metrics: len 240, pid: 0, seq 1, errno 0, flags:<UP,GATEWAY,STATIC>
locks:  inits:
sockaddrs: <DST,NETMASK,IFP>
 10.0.0.0 255.0.0.0 link#0
route: route has not been found

Note added RTA_NETMASK in the request.

Host address from the same network is ok:

route -nv get 10.0.0.1

RTA_DST: inet 10.0.0.1; RTA_IFP: link ; RTM_GET: Report Metrics: len 224, pid: 0, seq 1, errno 0, flags:<UP,GATEWAY,HOST,STATIC>
...
   route to: 10.0.0.1
destination: 10.0.0.0
       mask: 255.255.255.0

This is due to the logic that tries to "guess" netmask for the network-looking adresses by using long-forgotten functions like inet_lnaof().

The proposed change is simple: eliminate the entire guessing part and simplify the whole part.

route(8) manual suggests the following syntax variations are permitted (permutations with *-host* or *-net* flags skipped):

1. add 1.1.1.1 GW (treated as a host)
2. add 1.1.1.1 GW 255.255.0.0 (treated as a network)
3. add somehost.com GW (DNS resolve for a host)
4. add some_network GW (getnetbyname() reading /etc/networks and auto-guessing mask)
5. add some_network GW 255.255.255.0 OR some_netmask
6. add 1.1.1.1/32 GW

I propose to eliminate (4), (5) for the following reasons:

• rc.conf seem to be the master source of data for interface networks and static routes
• Again, modern way of storing static routes is either variations of rc.conf or the routing daemon.
• getnetbyname() does not support IPv6
• default handling assumes classful approach, which was deprecated 10+ years ago

The interesting part is how can we backport (any) of similar changes to solve the original problem, though..