MFC 228990,243232,243233:

Overhaul of route6d(8):

- Use queue(3) for linked-list.
- Use a consistent naming scheme for struct members.
- Use ANSI C style function declaration.
- Add check of RTM_VERSION mismatch.
- Increase the number of retry for NET_RT_DUMP from 5 to 15.
- Use 2001:db8:: as an example instead of deprecated 3ffe:: address block.
- Add check for connected routes.
- Add support of RTM_IFANNOUNCE for dyanmically-added/removed interfaces.
- Add support of *, ?, and [ in the interface list.
- Add -P number to specify route flag which will never expire.
- Add -Q number to specify route flag which route6d will add to routes via RIP.
- Add -p pidfile to specify the process ID file.